A car travels 150 km to the nearest km in 3 h to the nearest h. Find…

Step by step

The question

Question: A car goes 150 km (to the nearest km) in 3 h (to the nearest h).

Find the lower bound of the speed.

1 Bounds of each number

The distance is 150 km, to the nearest km.

Half a step is 0.5.

So it is from 149.5 up to 150.5.

The time is 3 h, to the nearest h.

Half a step is 0.5.

So it is from 2.5 up to 3.5.

2 Choose the bounds

Dividing by a bigger number gives a smaller answer.

So the smallest speed is the smallest distance divided by the biggest time.

So we use 149.5 and 3.5.

Careful!

A smaller bottom makes the answer bigger.

So the bottom goes the other way.

3 Work it out

With a calculator: about 42.7 km/h, to 3 significant figures.

So the lower bound of the speed is 42.7 km/h.

4 Check

Let's check.

With the rounded numbers we get 50.

The lower bound, 42.7, is less than that, as it should be.

So the answer is right!

Let's look back.

First: bounds of each number.

Then: choose the bounds.

Then: work it out.

Last: check.