alleryA man covers a distance in 6 hours at 40 km per hour. To cover it in 4 hours he must travel at:
A50 km per hour
B55 km per hour
C65 km per hour
D60 km per hour
Answer & Solution
Correct answer: D. 60 km per hour
1. First find the distance: 40 x 6 = 240 km.
2. The distance does not change, so speed and time are in inverse proportion.
3. The required speed is 240 / 4.
4. That is 60 km per hour.
5. Checking the ratio, the time fell to two thirds, so the speed must rise to three halves: 40 x 3 / 2 = 60.
_Source: syllabus Maths, Ch 11 'Direct and Inverse Proportions', S11.3 Inverse Proportion_
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