P6 Work backwards from volume or area
A square with area 100 cm²
A square has area 100 cm². Write its side length using square-root notation, then evaluate it.
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The pattern behind it: Work backwards from volume or area
Use the known area or volume to find the missing measurement.
In this one. A square has equal sides. Its side length is the positive square root of its area; this is different from dividing the area by two.
How to spot it
The question gives a cuboid's volume with two dimensions and asks for the third, or gives the volume with one length and asks for a face area. A square's area given with its side asked for belongs here too.
Common mistake
Children divide the volume by a length lying inside the face they want, instead of the length that runs into it, and get the wrong kind of measurement.
Try one like it
Standard A square with area 64 cm² A square has area 64 cm². Write its side length using square-root notation, then evaluate it.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.
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