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Published this.

#### Christian Lawson-Perfect7 years, 2 months ago

Gave some feedback: Ready to use

#### Christian Lawson-Perfect7 years, 2 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.

#### Stanislav Duris7 years, 2 months ago

Gave some feedback: Needs to be tested

#### Vicky Hall7 years, 2 months ago

Gave some feedback: Has some problems

#### Vicky Hall commented 7 years, 2 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.

#### Stanislav Duris7 years, 2 months ago

Gave some feedback: Needs to be tested

#### Elliott Fletcher commented 7 years, 2 months ago

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

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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.

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!

#### Elliott Fletcher7 years, 2 months ago

Gave some feedback: Has some problems

#### Stanislav Duris7 years, 2 months ago

Gave some feedback: Needs to be tested

#### Stanislav Duris7 years, 2 months ago

Created this.
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

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