KA-0064Fractions of a quantity
3 points, difficulty 1 of 3Level 5–6about 45sThree quarters of a class of 28 travelled by bus. How many did not travel by bus?
Hints
Take them one at a time. The first gives nothing away.
1A nudge
What fraction did not travel by bus?
2The strategy
If three quarters went by bus, the rest is one quarter. Taking one quarter of the class directly is one step; working out three quarters and subtracting is two.
3The full solution
One quarter of 28 is 7, so 7 students did not travel by bus.
Solution— no shortcut on this one
Three quarters went by bus, so one quarter did not. One quarter of 28 is 28 divided by 4 = 7. Check the other way: three quarters is 21, and 28 - 21 = 7. The transferable idea: when a question asks about the rest, find the fraction that is left over first — it is fewer steps and fewer chances to slip.
Why this is on the test: Answering with the quantity you computed rather than the one that was asked for is the single most common lost mark on the whole paper.