Estimating difficult questions

Example 1

Estimate `(108+387.3)/48`

`108` would be best estimated to the tens units to give `110`

`387.3` would be best estimated to the tens units to give `390`

`48` would be best rounded to `50`

The calculation would then be

`(110+390)/50`

which equals `500/50`

which equals `10`

The actual answer is `10.32` so we can see that `10` is a useful estimate.

Example 2

Estimate

`(38.3times50.4)/(5.1+4.98)`

`38.3` would be best rounded to `40`

`50.4` would be best rounded to `50`

`5.1` would be best rounded to `5`

`4.98` would also be best rounded to `5`

So the calculation becomes

`(40times50)/(5+5)`

We can work this out as `2000/10`

which equals `200`

The actual number is `191.5` so we can see that `200` is a useful estimate.