Question P3–P4–P5–P6 Working backwards
Today’s problem — free all day, every step. Every day has one.
Mei had some stickers in her sticker book. She traded with a friend, receiving 18 stickers and giving away 7 stickers. Then a bonus pack doubled the number of stickers in her book. She then had 60 stickers. How many stickers did she have before she traded with her friend?
Answer
See all 6 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.
I have a code → See the free ones
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. Work backwards by undoing the latest operation first: halve to undo the doubling, then subtract the trade’s net gain.
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.