Saturday, October 7, 2017

Revision: SST 2016 Maths S1 Paper 2 Q7

Given the speed of the following:
  • 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

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.

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