KA-0128Check units and re-read before bubbling
4 points, difficulty 2 of 3Level 5–6about 75sA rectangle measures 30 cm by 0.4 m. What is its area in square centimetres?
Hints
Take them one at a time. The first gives nothing away.
1A nudge
Put both sides in the same unit first.
2The strategy
Convert before multiplying, and check the direction: metres to centimetres makes the number bigger. Then check the unit the answer is wanted in before writing it down.
3The full solution
0.4 m is 40 cm, so the area is 30 x 40 = 1200 square centimetres.
Solution— no shortcut on this one
Convert first: 0.4 m is 0.4 x 100 = 40 cm - bigger, as changing to a smaller unit should be. Then the area is 30 x 40 = 1200 square centimetres. Check the unit asked for: square centimetres, which is what we have. The transferable idea: convert, calculate, then re-read the units in the question before writing the answer down.
Why this is on the test: Two of the five choices are right numbers in wrong units, which is exactly how this mark is lost in a real paper.