Today’s problem — free all day, every step. Every day has one.
Two pipes — filling a tank together
Pipe A can fill a tank in 6 hours. Pipe B can fill the same tank in 4 hours. Both pipes are turned on at the same time. How long will it take to fill the tank?
Show the answerHide the answer
See all 9 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 a free one like it
65 worked examples are free without a code, two from every pattern. No account, either way.
The pattern behind it: Number × value
One batch repeats. Work out one batch, then multiply.
In this one. You cannot add the times (6 h + 4 h means nothing here) — turn each time into a rate, how much of the tank is filled in one hour, because rates add and times do not.
Also uses: Same time, same distance
How to spot it
Items are described as a fixed group or ratio that repeats, such as tiles following a pattern, snacks sold in a fixed mix, or a rate given per hour or per item.
Common mistake
Children start from the grand total instead of first working out what one batch is worth. In rate questions they also confuse a duration with a clock time.
Try one like it
Standard Buns and muffins — 3 : 5 worth $55 A bakery sells buns and muffins in the ratio of 3 buns to 5 muffins. Each bun costs $2, and each muffin costs $1. If the total val…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.