x = 6.3 and y = 1.8, both to 1 decimal place. Find the lower bound…

Step by step

The question

Question: x = 6.3 and y = 1.8, both to 1 decimal place.

Find the lower bound of x ÷ y.

1 Bounds of each number

The number x is 6.3, to 1 decimal place.

Half a step is 0.05.

So it is from 6.25 up to 6.35.

The number y is 1.8, to 1 decimal place.

Half a step is 0.05.

So it is from 1.75 up to 1.85.

2 Choose the bounds

Dividing by a bigger number gives a smaller answer.

So the smallest answer is the smallest x divided by the biggest y.

So we use 6.25 and 1.85.

Careful!

A smaller bottom makes the answer bigger.

So the bottom goes the other way.

3 Work it out

With a calculator: about 3.38, to 3 significant figures.

So the lower bound of the answer is 3.38.

4 Check

Let's check.

With the rounded numbers we get 3.5.

The lower bound, 3.38, 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.