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P4–P5–P6 Suppose and swap

Today’s problem — free all day, every step. Every day has one.

Market stall baskets — small and large, loaves of bread

A bakery packs 15 baskets of bread for a market stall. Each small basket holds 3 loaves and each large basket holds 5 loaves. Altogether the baskets hold 51 loaves. How many large baskets are there?

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There are 3 large baskets and 12 small baskets. Check: 3 + 12 = 15 baskets, and 3 × 5 + 12 × 3 = 15 + 36 = 5…

One step of the worked solution to Market stall baskets — small and large, loaves of bread, drawn in pencil.
5 steps, drawn in pencil

The pattern behind it: Suppose and swap

Suppose everything is one kind, then swap one at a time until the total is right.

In this one. Assume every basket is the smaller type, find the shortfall, then divide by the fixed increase from changing one small basket into one large basket.

All 30 chickens60 legs, 36 short of 96legseach box is 12 legsEach swapa chicken out, a cow inadds2 legs — 36 ÷ 2 = 18 cows

How to spot it

Two kinds of thing are mixed together with a known total count and a known total of something else, such as legs or sweets, and neither kind's count is given on its own.

Common mistake

Children lose track of whether a swap adds to the total or takes away from it. Compare the starting total with the target first, then swap in the direction that closes the gap.

Try one like it

Standard Bicycles and tricycles — 58 wheels A cycling club has 25 vehicles parked outside, a mix of bicycles and tricycles. Bicycles have 2 wheels and tricycles have 3 wheels…
All 13 with this pattern →

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.