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Stanislav Duris 2 years, 2 months ago
I've changed the percentages to be multiples of 5 and adjusted the advice.
I believe the line in the advice about not rouding can be correct. This is because in case the third decimal place of the calculated discount is 5 and all the following decimal places are zeros (so it would be xxx.xx5), we would round up and therefore subtract this rounded up value. However, the shop would technically round this down as they calculate the price by simply multiplying the original price by the percentage and they would round up there, cause they would also get 5 as the third decimal place and the rest would be zeros. So rounding the discount results in an error of 1 penny in some cases
This happened on occasions with previous percentages but seems not to happen anymore with multiples of 5 so I removed that line.
Christian Lawson-Perfect 2 years, 2 months ago
Saved a checkpoint:
I don't think anyone in the history of shopping has had a voucher for a 12% discount. Pick multiples of 5%.
The line in the advice about not rounding until the end is incorrect - in this instance you can round off the discount before subtracting it from the original price. If you were subtracting two discounts, or performing a further calculation with the discounted price, you might encounter problems.
"This does not make sense in the real world" needs to be more precise - something like "The shop would round this discount to the nearest penny" would do.
I don't think I agree with "Method 1 is a bit simpler and more appropriate to use." - simplicity is in the eye of the beholder! Just briefly describe each method instead: "the first method involves working out the discounted price as a percentage of the original, while the second method calculates the value of the discount and subtracts that from the listed price."
Bradley Bush 2 years, 2 months ago
Very good, straight forward question so only a few minor ideas:
- I know you've said it in the advice but you probably should specify that you want rounding to 2 decimal places (or the nearest penny) particularly because sometimes shops will round up the cost of an item etc.
- If you were able to, a warning message that explains the figure needs to be rounded to 2.d.p might be really useful for cases where students have put the full length answer in.
- On the rounding note, in the advice, it would probably be useful to have the full non-rounded answer then have a extra step where the figure is rounded to 2.d.p.
- I think that it is very thorough that you've included both methods of finding the solution using both fractionas and decimals aswell, so well done for that.
Really good question overall
Vicky Hall 2 years, 3 months ago
Parts b) and d) are testing subtraction rather than percentages so remove these parts. If you wanted to bulk out questions you could combine the ideas in parts a), c) and d) into a single question. Some questions giving the new price after the percentage change and asking students to calculate the old price would be good here to demonstrate that it matters which number you take the percentage of (this often confuses students). It would also be a good idea to have students calculate the percentage change bewteen two prices.
In the advice, I would include mulipliers as one of your possible methods for calculating percentages. For example, to find $25%$ we can mulitply by $0.25$. To increase something by $10%$, we can multiply by $1.1$.
|Calculate a student discount||Ready to use||Stanislav Duris||01/08/2017 14:30|
|Stanislav's copy of Calculate decreasing and increasing costs using percentages needs to be tested||Should not be used||Stanislav Duris||22/06/2017 14:27|
|Calculate a student discount||Should not be used||Stanislav Duris||22/06/2017 16:19|
|Calculate the original price before a decrease||Ready to use||Stanislav Duris||14/08/2017 12:24|
|Consumer Arithmetic - Calculate the original price before a decrease||draft||Paul Hancock||24/07/2018 02:53|
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