// Numbas version: finer_feedback_settings
{"name": "Solving exponential equations using logs", "extensions": [], "custom_part_types": [], "resources": [], "navigation": {"allowregen": true, "showfrontpage": false, "preventleave": false, "typeendtoleave": false}, "question_groups": [{"pickingStrategy": "all-ordered", "questions": [{"variable_groups": [{"variables": ["FV", "pay", "int", "periods", "test"], "name": "b"}], "preamble": {"js": "", "css": ""}, "ungrouped_variables": ["a", "p", "c", "b", "frac", "logfrac", "logb", "d", "amc", "n"], "functions": {}, "extensions": [], "variablesTest": {"condition": "", "maxRuns": 100}, "metadata": {"description": "", "licence": "Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International"}, "statement": "", "variables": {"int": {"templateType": "anything", "description": "", "definition": "random(0.01..0.10#0.01)", "group": "b", "name": "int"}, "n": {"templateType": "anything", "description": "", "definition": "d*logfrac/logb", "group": "Ungrouped variables", "name": "n"}, "test": {"templateType": "anything", "description": "", "definition": "fv*int/pay", "group": "b", "name": "test"}, "amc": {"templateType": "anything", "description": "", "definition": "a-c", "group": "Ungrouped variables", "name": "amc"}, "p": {"templateType": "anything", "description": "", "definition": "random(2,5,10,20,(a-c)/2,(a-c)/5,(a-c)/10,(a-c)/20)", "group": "Ungrouped variables", "name": "p"}, "FV": {"templateType": "anything", "description": "", "definition": "random(20000..100000#500)", "group": "b", "name": "FV"}, "c": {"templateType": "anything", "description": "", "definition": "random(20..a-10#20)", "group": "Ungrouped variables", "name": "c"}, "frac": {"templateType": "anything", "description": "", "definition": "(a-c)/p", "group": "Ungrouped variables", "name": "frac"}, "b": {"templateType": "anything", "description": "", "definition": "random(1.05..1.5#0.05)", "group": "Ungrouped variables", "name": "b"}, "a": {"templateType": "anything", "description": "", "definition": "random(1000..2000#20)", "group": "Ungrouped variables", "name": "a"}, "d": {"templateType": "anything", "description": "", "definition": "random(2,4,3,12,26,52)", "group": "Ungrouped variables", "name": "d"}, "periods": {"templateType": "anything", "description": "", "definition": "log(FV*int/pay+1)/log(1+int)", "group": "b", "name": "periods"}, "logfrac": {"templateType": "anything", "description": "", "definition": "log(frac)", "group": "Ungrouped variables", "name": "logfrac"}, "pay": {"templateType": "anything", "description": "", "definition": "random(100..2000#100)", "group": "b", "name": "pay"}, "logb": {"templateType": "anything", "description": "", "definition": "log(b)", "group": "Ungrouped variables", "name": "logb"}}, "tags": [], "parts": [{"customName": "", "customMarkingAlgorithm": "", "sortAnswers": false, "scripts": {}, "prompt": "<p>Solve the following equation for $n$</p>\n<p style=\"text-align: left;\">$\\displaystyle{\\simplify{{a}={p}({b})^(n/{d})+{c}}}.$</p>\n<p style=\"text-align: center;\"></p>\n<p style=\"text-align: left;\">$n=$&nbsp;[[0]]</p>\n<p style=\"text-align: left;\"><strong></strong></p>\n<p style=\"text-align: left;\"><strong>Note:</strong><span>&nbsp;Typing $\\log(5)$&nbsp;will input the value&nbsp;$\\log_{10}(5)$, whereas&nbsp;$\\log5$ will not work.<br/><strong>Note:&nbsp;</strong>Typing $\\ln(5)$ will input the value $\\log_e(5)$, whereas $\\ln5$ will not work.</span></p>", "stepsPenalty": "1", "extendBaseMarkingAlgorithm": true, "showCorrectAnswer": true, "variableReplacementStrategy": "originalfirst", "type": "gapfill", "steps": [{"customName": "", "customMarkingAlgorithm": "", "scripts": {}, "prompt": "<p>We start solving the equation one operation at a time by doing the inverse to both sides, when we get to undoing the exponential we apply a log to both sides, we then use a log law and continue solving.</p>\n<p></p>\n<table>\n<tbody>\n<tr>\n<td style=\"text-align: right;\">$\\var{a}$</td>\n<td style=\"text-align: center;\">$=$</td>\n<td style=\"text-align: left;\">$\\simplify{{p}({b})^(n/{d})+{c}}$</td>\n<td style=\"text-align: left;\"></td>\n</tr>\n<tr>\n<td style=\"text-align: right;\">$\\simplify{{a-c}}$</td>\n<td style=\"text-align: center;\">$=$</td>\n<td style=\"text-align: left;\">$\\simplify{{p}({b})^(n/{d})}$</td>\n<td style=\"text-align: left;\">(subtract $\\var{c}$ from both sides)&nbsp;</td>\n</tr>\n<tr>\n<td style=\"text-align: right;\">$\\var{frac}$</td>\n<td style=\"text-align: center;\">$=$</td>\n<td style=\"text-align: left;\">$\\simplify{{b}^(n/{d})}$</td>\n<td style=\"text-align: left;\">(divide both sides by $\\var{p}$)</td>\n</tr>\n<tr>\n<td style=\"text-align: right;\">$\\log(\\var{frac})$</td>\n<td style=\"text-align: center;\">$=$</td>\n<td style=\"text-align: left;\">$\\log(\\var{b}^{\\frac{n}{\\var{d}}})$</td>\n<td style=\"text-align: left;\">(take the log of both sides)</td>\n</tr>\n<tr>\n<td style=\"text-align: right;\"></td>\n<td style=\"text-align: center;\">$=$&nbsp;</td>\n<td style=\"text-align: left;\">$\\frac{n}{\\var{d}}\\log(\\var{b})$</td>\n<td style=\"text-align: left;\">(use a log law)</td>\n</tr>\n<tr>\n<td style=\"text-align: right;\"></td>\n<td style=\"text-align: center;\"></td>\n<td style=\"text-align: left;\"></td>\n<td style=\"text-align: left;\"></td>\n</tr>\n<tr>\n<td style=\"text-align: right;\">$\\displaystyle{\\frac{\\log(\\var{frac})}{\\log(\\var{b})}}$</td>\n<td style=\"text-align: center;\">$=$</td>\n<td style=\"text-align: left;\">$\\frac{n}{\\var{d}}$</td>\n<td style=\"text-align: left;\">(divide both sides by $\\log(\\var{b})$)</td>\n</tr>\n<tr>\n<td style=\"text-align: right;\"></td>\n<td style=\"text-align: center;\"></td>\n<td style=\"text-align: left;\"></td>\n<td style=\"text-align: left;\"></td>\n</tr>\n<tr>\n<td style=\"text-align: right;\">$\\displaystyle{\\frac{\\var{d}\\log(\\var{frac})}{\\log(\\var{b})}}$</td>\n<td style=\"text-align: center;\">$=$</td>\n<td style=\"text-align: left;\">$n$</td>\n<td style=\"text-align: left;\">(multiply both sides by $\\var{d}$)</td>\n</tr>\n</tbody>\n</table>\n<p></p>", "extendBaseMarkingAlgorithm": true, "showCorrectAnswer": true, "variableReplacementStrategy": "originalfirst", "type": "information", "showFeedbackIcon": true, "marks": 0, "unitTests": [], "useCustomName": false, "variableReplacements": []}], "showFeedbackIcon": true, "marks": 0, "unitTests": [], "useCustomName": false, "gaps": [{"customName": "", "customMarkingAlgorithm": "", "scripts": {}, "failureRate": 1, "answer": "{d}*log({frac})/log({b})", "valuegenerators": [], "checkingType": "absdiff", "extendBaseMarkingAlgorithm": true, "showCorrectAnswer": true, "variableReplacementStrategy": "originalfirst", "type": "jme", "vsetRange": [0, 1], "showFeedbackIcon": true, "marks": 1, "vsetRangePoints": 5, "checkVariableNames": false, "unitTests": [], "showPreview": true, "useCustomName": false, "variableReplacements": [], "checkingAccuracy": 0.001}], "variableReplacements": []}, {"customName": "", "customMarkingAlgorithm": "", "sortAnswers": false, "scripts": {}, "prompt": "<p>Solve the following equation for $n$</p>\n<p style=\"text-align: left;\">$\\displaystyle{\\simplify{{FV}={pay}((1+{int})^n-1)/{int}}}.$</p>\n<p style=\"text-align: center;\"></p>\n<p style=\"text-align: left;\">$n=$&nbsp;[[0]]</p>\n<p style=\"text-align: left;\"><strong></strong></p>\n<p style=\"text-align: left;\"><strong>Note:</strong><span>&nbsp;Typing $\\log(5)$&nbsp;will input the value&nbsp;$\\log_{10}(5)$, whereas&nbsp;$\\log5$ will not work.<br/><strong>Note:&nbsp;</strong>Typing $\\ln(5)$ will input the value $\\log_e(5)$, whereas $\\ln5$ will not work.</span></p>", "stepsPenalty": "1", "extendBaseMarkingAlgorithm": true, "showCorrectAnswer": true, "variableReplacementStrategy": "originalfirst", "type": "gapfill", "steps": [{"customName": "", "customMarkingAlgorithm": "", "scripts": {}, "prompt": "<p>We start solving the equation one operation at a time by doing the inverse to both sides, when we get to undoing the exponential we apply a log to both sides, we then use a log law and continue solving.</p>\n<p></p>\n<table>\n<tbody>\n<tr>\n<td style=\"text-align: right;\">${\\var{FV}}$</td>\n<td style=\"text-align: center;\">$=$</td>\n<td style=\"text-align: left;\">$\\displaystyle{\\simplify{{pay}((1+{int})^n-1)/{int}}}$</td>\n<td style=\"text-align: left;\"></td>\n</tr>\n<tr>\n<td style=\"text-align: right;\">$\\simplify{{FV*int}}$</td>\n<td style=\"text-align: center;\">$=$</td>\n<td style=\"text-align: left;\">$\\displaystyle{\\simplify{{pay}((1+{int})^n-1)}}$</td>\n<td style=\"text-align: left;\">(multiply both sides by&nbsp;$\\var{int}$)&nbsp;</td>\n</tr>\n<tr>\n<td style=\"text-align: right;\">$\\displaystyle{\\simplify[simplifyFractions]{{FV*int}/{pay}}}$</td>\n<td style=\"text-align: center;\">$=$</td>\n<td style=\"text-align: left;\">$\\displaystyle{\\simplify{(1+{int})^n-1}}$</td>\n<td style=\"text-align: left;\">(divide both sides by $\\var{pay}$)</td>\n</tr>\n<tr>\n<td style=\"text-align: right;\">$\\displaystyle{\\simplify[simplifyFractions]{{FV*int}/{pay}+1}}$</td>\n<td style=\"text-align: center;\">$=$</td>\n<td style=\"text-align: left;\">$\\displaystyle{\\simplify{(1+{int})^n}}$</td>\n<td style=\"text-align: left;\">(add $1$ to both sides)</td>\n</tr>\n<tr>\n<td style=\"text-align: right;\">$\\displaystyle{\\simplify[simplifyFractions]{{FV*int+pay}/{pay}}}$</td>\n<td style=\"text-align: center;\">$=$&nbsp;</td>\n<td style=\"text-align: left;\">$\\displaystyle{\\simplify{(1+{int})^n}}$</td>\n<td style=\"text-align: left;\">(tidy up left hand side)</td>\n</tr>\n<tr>\n<td style=\"text-align: right;\"></td>\n<td style=\"text-align: center;\"></td>\n<td style=\"text-align: left;\"></td>\n<td style=\"text-align: left;\"></td>\n</tr>\n<tr>\n<td style=\"text-align: right;\">$\\displaystyle{\\log\\left(\\simplify[simplifyFractions]{{FV*int+pay}/{pay}}\\right)}$</td>\n<td style=\"text-align: center;\">$=$</td>\n<td style=\"text-align: left;\">$\\displaystyle{\\log\\left((\\var{1+int})^n\\right)}$</td>\n<td style=\"text-align: left;\">(take the log of both sides)</td>\n</tr>\n<tr>\n<td style=\"text-align: right;\"></td>\n<td style=\"text-align: center;\"></td>\n<td style=\"text-align: left;\"></td>\n<td style=\"text-align: left;\"></td>\n</tr>\n<tr>\n<td style=\"text-align: right;\">$\\displaystyle{\\log\\left(\\simplify[simplifyFractions]{{FV*int+pay}/{pay}}\\right)}$</td>\n<td style=\"text-align: center;\">$=$</td>\n<td style=\"text-align: left;\">$\\displaystyle{n\\log(\\var{1+int})}$</td>\n<td style=\"text-align: left;\">(use a log law)</td>\n</tr>\n<tr>\n<td style=\"text-align: right;\"></td>\n<td style=\"text-align: center;\"></td>\n<td style=\"text-align: left;\"></td>\n<td style=\"text-align: left;\"></td>\n</tr>\n<tr>\n<td style=\"text-align: right;\">$\\displaystyle{\\frac{\\log\\left(\\simplify[simplifyFractions]{{FV*int+pay}/{pay}}\\right)}{\\log(\\var{1+int})}}$</td>\n<td style=\"text-align: center;\">$=$</td>\n<td style=\"text-align: left;\">$n$</td>\n<td style=\"text-align: left;\">(divide both sides by $\\log(\\var{1+int})$)</td>\n</tr>\n</tbody>\n</table>\n<p></p>", "extendBaseMarkingAlgorithm": true, "showCorrectAnswer": true, "variableReplacementStrategy": "originalfirst", "type": "information", "showFeedbackIcon": true, "marks": 0, "unitTests": [], "useCustomName": false, "variableReplacements": []}], "showFeedbackIcon": true, "marks": 0, "unitTests": [], "useCustomName": false, "gaps": [{"customName": "", "customMarkingAlgorithm": "", "failureRate": 1, "checkingType": "absdiff", "showCorrectAnswer": true, "checkVariableNames": false, "vsetRange": [0, 1], "showFeedbackIcon": true, "vsetRangePoints": 5, "checkingAccuracy": 0.001, "scripts": {}, "answer": "log({FV*int+pay}/{pay})/log({1+int})", "valuegenerators": [], "extendBaseMarkingAlgorithm": true, "variableReplacementStrategy": "originalfirst", "type": "jme", "answerSimplification": "simplifyFractions", "marks": 1, "unitTests": [], "showPreview": true, "useCustomName": false, "variableReplacements": []}], "variableReplacements": []}], "rulesets": {}, "advice": "", "name": "Solving exponential equations using logs", "type": "question", "contributors": [{"name": "Ben Brawn", "profile_url": "https://numbas.mathcentre.ac.uk/accounts/profile/605/"}, {"name": "Xiaodan Leng", "profile_url": "https://numbas.mathcentre.ac.uk/accounts/profile/2146/"}]}]}], "contributors": [{"name": "Ben Brawn", "profile_url": "https://numbas.mathcentre.ac.uk/accounts/profile/605/"}, {"name": "Xiaodan Leng", "profile_url": "https://numbas.mathcentre.ac.uk/accounts/profile/2146/"}]}