- Adam 160 m/min
- Bernard 120 m/min
Strategy: Put all information in a diagram and draw 'relationships' (with reference to the speed-time-distance formula) to form equations
Since we do not know the distance for the race, let it be d metres.
Since we are not given the time taken by Adam to complete the race, let the time taken be t minutes.
The 2nd diagram shows the position of Adam, Bernard and Charlie at t minutes.
Hence, what's common for all three boys is the duration, t minutes.
Using the formula, Distance = Speed x Time
With this, we know that distance covered by Charlie (at t min) = 800 m - 250 m = 550 m
Substitute d = 550 into first equation (i.e. time taken by Adam), we have
Time taken, t = 800 ÷ 150 = 5 minutes
Hence, Charlie's speed
= Distance covered/ Time taken
= 550 m ÷ 5 min
= 110 m/min (Ans)
Note: There are other 'shortcuts' to solve the problem. However, the above will give you an idea how to solve the unknown(s) systematically using the known relationships for speed-time-distance.