Mammoth Memory

Estimating and rounding

Choosing where to round will help you estimate more easily.

Choosing where to round will make estimates more easier to make 

You said it was only going to be a few dollars.


Example 1

Where would you estimate $`59.41`

The choice would be

Round to the `1^(st)` decimal place `59.40`
Round to the units of 1 column `59.00`
Round to the tens units `60.00`

You can see that rounding to the tens units i.e. $`60.00` is not too far from $`59.41` and is clearly easier to remember.


Example 2

The attendance at a football match is 34,846 people, how would you estimate this in order to tell your friends the attendance?

The choice would be

Round to the tens units `34,850`
Round to the hundreds units `34,800`
Round to the thousands  `35,000`
Round to the tens of thousands  `30,000`

You can see that the most representative estimate would be `35,000` and would only be `154` out from the original number.


Example 3

Bernice decides to go shopping and in her trolley, she has two shirts for `£10.99`, three skirts for `£21.20` and a pair of shoes for `£69.00` She has `£180`. Estimate the value of the clothes to decide if she has enough.

Adding `2times£10.99`
`+` `3times£21.20`
`+` `1times£69.00`

is tough

But adding `2times£10`
`+` `3times£20`
`+` `1times£70`

is a lot easier

`2times£10` `=£20`
`3times£20` `=£60`
`1times£70` `=£70`

She has enough



The real answer is `£154.58` but the estimate of `£150` is enough to realise that `£180` is sufficient to purchase all the clothes.


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