MathBrush
←  All problems

Question P6 Repeated identity

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

A tray of ice blocks — large and small

A caterer packs a rectangular tray-box tightly with 12 identical large ice blocks and some identical small ice cubes, so that cubes of the same size are stacked directly on top of each other, filling the box exactly to the brim. The figure shows the first layer of cubes packed in the box.

  1. (a) How many small ice cubes does the caterer have?
  2. (b) The volume of the box is 1536 cm³. The total volume of the 12 large ice blocks is of the volume of the box. What is the length of one edge of the small ice cube?
The first layer of the box seen from above: 6 large ice blocks on the left and 24 small ice cubes on the right, both blocks running the full depth of the box. Drawn to scale.

See all 10 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.

About this method

Repeated identity

One length or count, described two ways in the same question.

In this one. The picture gives no lengths at all, but two large cubes and four small ones fill the same depth — that pins L : s = 2 : 1, and once the two cubes are tied together the whole box can be counted in cube-layers long before any measurement appears.

the same edge, measured twicelong tilesshort tilesboth rows end level, so 3 long = 5 short

How to spot it

A shape or count is described from two viewpoints in the same question, such as one edge measured as a number of long pieces and again as a number of short pieces.

Common mistake

Children treat the two descriptions as separate quantities and add them. Both describe the same quantity, so the two must be equal.

Practise a similar question

Standard A rectangular tank measures 30 cm by 20 cm by 25 cm. It is 3/5 full of water. All the water is poured into a second rectangular container with a base area of 200 cm². What is the height of the water in the second contain…
All 16 with this pattern →
Get the free patterns and skills booklet

Patterns and skills booklet

Worked examples of all 33 patterns and skills, in a booklet you can print.