KA-0117Rate, time, distance
4 points, difficulty 2 of 3Level 5–6about 75sA train covers 150 km at a steady 60 km per hour. How many minutes does the journey take?
Hints
Take them one at a time. The first gives nothing away.
1A nudge
Find the time in hours first.
2The strategy
Time is distance divided by speed, which gives an answer in hours. Convert to minutes only at the end, and check the size of the number after converting.
3The full solution
150 divided by 60 is 2.5 hours, and 2.5 x 60 = 150 minutes.
Solution— no shortcut on this one
Time is distance divided by speed: 150 divided by 60 = 2.5 hours. The question asks for minutes, so convert at the end: 2.5 x 60 = 150 minutes. It is a coincidence that the answer in minutes matches the distance in kilometres, which is exactly why the working matters more than the number. The transferable idea: compute in the natural unit, convert last, and check the answer's size after converting.
Why this is on the test: A coincidence between two numbers in the question makes it easy to arrive at the right answer for the wrong reason, and the unit conversion is the real test.