Today’s problem — free all day, every step. Every day has one.
find a starting time
An activity ended at 10:20 after 75 minutes. When did it start?
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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.
The pattern behind it: Working backwards
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.
How to spot it
The question gives the final amount after a sequence of changes and asks what the amount was 'at first' or 'to begin with'.
Common mistake
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%.
Try one like it
Standard find a starting time An activity ended at 14:10 after 50 minutes. When did it start?The 33 problem patterns
All 33 patterns, one to a page — the 19 behind Primary 5 and 6 word problems, and the skills the younger years are built on. The bar model, how to spot it in the question, and the mistake children make. A booklet you can print. Free.
A PDF, and a note when new solutions go up.