My dc has come across a question in the Bond Practice Test Maths 11+, which is included in the Bond How to do... Maths book.
Q 50. A door is 5 feet 9 inches high. Which is the closest to its height in meters? Circle the correct answer.
the options are 1.5m 1.6m 1.7m 1.8m 1.9m
Bearing in mind that our dc are taking their respectice tests at the end of Year 5, are they really expected to know the conversion of Imperial to Metric units data?
It's in KS2 (cf http://goo.gl/JK5GI
But that's a shocking question, because the answer hinges on the precision of the conversion factor you use. The correct value is 2.54cm = 1" (because a yard is now defined to be 0.9144m), so 69 x 2.54 = 1.7526m, making the answer 1.8m. But if you use the typical KS2 conversion factor of 2.5cm ~ 1", you get 69 x 2.5 = 1.725m, making the answer 1.7m. 2.5cm ~ 1" is off by nearly 0.5cm per foot, hence the near-3cm difference. It's a pretty fundamental law of setting multiple-choice questions which permit an approximation that the candidate gets credit for providing the correct answer as well.