Video: Pack 1 • Paper 3 • Question 12

Pack 1 • Paper 3 • Question 12


Video Transcript

A car travelled a distance of 43.7 kilometres. It travelled at a speed of 532 metres per minute. How long was the car travelling for? Round your answer to two significant figures.

To answer this question, we need to recall the formula triangle that connects the three quantities speed, distance, and time. By covering up the quantity we wish to calculate, so in this question that’s the time, we can see the formula that we need to use: time is equal to distance divided by speed.

The distance travelled and the speed are both given in the question. But if we look carefully, we can see that the length units used are different: for distance, it’s kilometres, whereas for speed, it’s metres. Before we can answer this question, we need to convert to the same unit. So we we’ll convert the distance of 43.7 kilometres into metres.

To do so, we need to recall that one kilometre is equal to 1000 metres. So to convert 43.7 kilometres into metres, we multiply by 1000. 43.7 multiplied by 1000 is 43700. The calculation for the time taken is, therefore, 43700 divided by 532. And we can use our calculator to evaluate this. It’s equal to 82.142857 and the decimal continues.

Now, the question asked us to round our answer to two significant figures. And read that carefully — it’s significant figures, not decimal places. The first significant figure is the first nonzero digit in the number. So in this case, that’s eight. The second significant figure is the next digit two. We need to look at one more figure in the number to determine whether we should be rounding up or down. And as the next digit is a one, this tells us that we’re rounding down. This gives a value of 82 and the units for this time are minutes.

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