Question P3 Working backwards
Today’s problem — free all day, every step. Every day has one.
An activity ended at 10:20 after 75 minutes. When did it start?
Answer
See all 5 steps
MathBrush is being tested with a few parent groups, and every solution on the site is open to them — one household, all children. If you were given a code, it goes in once and this device remembers it.
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65 worked examples are free without a code, two from every pattern. No account, either way.
You know how it ended. Undo each step, last one first.
In this one. Starting time is found by subtracting the elapsed duration from finishing time.
The question gives the final amount after a sequence of changes and asks what the amount was 'at first' or 'to begin with'.
Children undo the steps in the same order they happened rather than in reverse, or forget that a percentage profit is added to the cost price, so the final price is 120% of it, not 100%.
Worked examples of all 33 patterns and skills, in a booklet you can print.