Simple interest

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From users who are members of Transition to university :

Christian Lawson-Perfect	said	Ready to use	7 years, 8 months ago
Stanislav Duris	said	Needs to be tested	7 years, 9 months ago
Vicky Hall	said	Has some problems	7 years, 9 months ago
Elliott Fletcher	said	Has some problems	7 years, 9 months ago

History

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Stanislav Duris 7 years, 8 months ago

Published this.

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Christian Lawson-Perfect 7 years, 8 months ago

Gave some feedback: Ready to use

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Christian Lawson-Perfect 7 years, 8 months ago

Saved a checkpoint:

I've changed some of the wording, and used dpformat to make sure currency amounts are always shown to two decimal places. A good, simple question.

Restore this checkpoint

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Stanislav Duris 7 years, 9 months ago

Gave some feedback: Needs to be tested

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Vicky Hall 7 years, 9 months ago

Gave some feedback: Has some problems

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Vicky Hall commented 7 years, 9 months ago

I think this should be split into two questions, one on simple interest calculations and the other on compound interest calculations (which I would actually call exponential increase and decrease - if you consider your mobile phone question, there is no interest involved).

The question on exponential increase and decrease could potentially have three subparts to fully cover the subject. The first part would be the mobile phone question as it stands. Secondly, you could ask after how many months will the phone be worth £ $x$ ? Thirdly, if a different phone was originally worth £ $y$ and after $z$ months it is worth £ $w$ , by what percentage did its value decrease each month?

In the steps for calculating compound interest, it would be better to finish by showing that if we decrease something by $5$ % three times, this is the same as multiplying by $0.95\times0.95\times0.95=0.95^3$ . Showing students how to work with powers could save them a lot of time if the increase/decrease needs to be performed several times, plus it gives them a way to solve variations on the question.

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Stanislav Duris 7 years, 9 months ago

Gave some feedback: Needs to be tested

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Elliott Fletcher commented 7 years, 9 months ago

I think this is a good question, it is reasonably challenging and well constructed.

Main Parts

a), b) I think you should add a hint for the precision required, even though i know the units are in pounds and there only should be two decimal places, but i would still include a hint saying give your answer to two decimal places.

b) i'm not entirely sure about this but i don't think the steps you give here are entirely relevant, as the steps show an increase in money every year whereas the question is about money decreasing monthly.

Advice

a) I would say "This is the money we would get if we withdrew the whole savings balance today" instead

b) you have an & where there should be a %

When you say "we multiply the original price of the smartphone by our multipliers 12 times", i think this should be "multiplier" (singular) and then "as there are 12 months in a year" rather than "as there is 12 months in a year"

a) and b) i think you should add a £ symbol to your final answers in the advice section just to make it clear that this is an amount of money.

Otherwise, this looks pretty good!

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Elliott Fletcher 7 years, 9 months ago

Gave some feedback: Has some problems

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Stanislav Duris 7 years, 9 months ago

Gave some feedback: Needs to be tested

○

Stanislav Duris 7 years, 9 months ago

Created this.

Name	Status	Author	Last Modified
Simple interest	Ready to use	Stanislav Duris	20/11/2019 14:42
Cumulative percent decrease	Ready to use	Stanislav Duris	20/11/2019 14:36
Exponential increase	Ready to use	Stanislav Duris	20/11/2019 14:38
Ida's copy of Cumulative percent decrease	draft	Ida Landgärds	12/04/2018 10:54
Spørsmål 4	draft	Ida Landgärds	02/12/2020 15:42
haifa's copy of Cumulative percent decrease	draft	haifa abd	01/05/2018 14:20
Consumer Arithmetic - Simple Interest	draft	Paul Hancock	24/07/2018 03:08

There are 9 other versions that do you not have access to.

Question statement

Suppose you put £{money} into a savings account exactly {years} years ago and you haven't touched the money since. The simple interest rate on the account is {perc2}% per year.

Give any introductory information the student needs.

			Name	Type	Generated Value

perc2	number	1.25
money	integer	1400
years	integer	6

Automatically regenerate variables?

Name

Data type

Value

xxxxxxxxxx
 
random(0..2.5 #0.05)

JME function reference

Description

Describe what this variable represents, and list any assumptions made about its value.

Can an exam override the value of this variable?

Generated value: `number`

1.25

This variable doesn't seem to be used anywhere.

Parts

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1. Gap Number entry
  Add

Gap-fill

Ask the student a question, and give any hints about how they should answer this part.

If you were to withdraw the money from this account now, how much would you have?

£ Unnamed gap

Advice

This is simple interest, which means the amount added each year is a percentage of the original amount. The amount we add is fixed for all {years} years.

First, we work out the amount of interest for one year:

$\begin{align} \var{perc2} \text{% of } \var{money} &= \frac{\var{perc2}}{100} \times \var{money} \\ &= \var{perc2/100} \times \var{money} \\ &= £\var{dpformat(perc2/100*money,2)} \text{.} \end{align}$

The money has been in the account for {years} years, so we multiply $£\var{dpformat(perc2/100*money,2)}$ by $\var{years}$ .

$£\var{dpformat(perc2/100*money,2)} \times \var{years} = £\var{dpformat(perc2/100*money*years,2)} \text{.}$

Adding this to the original balance:

$£\var{money} + £\var{dpformat(perc2/100*money*years,2)} = £\var{dpformat(perc2/100*money*years + money,2)} \text{.}$

This is the amount we would get if we withdrew the whole savings balance today.

Give a worked solution to the whole question.

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Part	Test	Passed?
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Gap-fill		Hasn't run yet
Number entry
Number entry		Hasn't run yet

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Checkpoint description

Stanislav Duris 7 years, 8 months ago

Christian Lawson-Perfect 7 years, 8 months ago

Christian Lawson-Perfect 7 years, 8 months ago

Stanislav Duris 7 years, 9 months ago

Vicky Hall 7 years, 9 months ago

Vicky Hall commented 7 years, 9 months ago

Stanislav Duris 7 years, 9 months ago

Elliott Fletcher commented 7 years, 9 months ago

Elliott Fletcher 7 years, 9 months ago

Stanislav Duris 7 years, 9 months ago

Stanislav Duris 7 years, 9 months ago

Error in variable testing condition

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Generated value: `number`

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Simple interest

Metadata

Taxonomy: mathcentre

Taxonomy: Kind of activity

Taxonomy: Context

Contributors

Feedback

History

Comment

Checkpoint description

Stanislav Duris 7 years, 8 months ago

Christian Lawson-Perfect 7 years, 8 months ago

Christian Lawson-Perfect 7 years, 8 months ago

Stanislav Duris 7 years, 9 months ago

Vicky Hall 7 years, 9 months ago

Vicky Hall commented 7 years, 9 months ago

Stanislav Duris 7 years, 9 months ago

Elliott Fletcher commented 7 years, 9 months ago

Elliott Fletcher 7 years, 9 months ago

Stanislav Duris 7 years, 9 months ago

Stanislav Duris 7 years, 9 months ago

Error in variable testing condition

Error

Warning

Generated value: number

Parts

Gap-fill

Generated value: `number`