# Cluster estimating

Cluster estimating is finding a common centre in a group of numbers.

There is a beautiful nut cluster in the centre of this chocolate bar.

Example 1

Add 357+343+355+345+356

If you rounded each of these numbers to the tens column you would get.

360+340+360+350+360

But if you realise the numbers were roughly clustered around 350 i.e.

350+350+350+350+350

5times350 is far easier to work out

5times350=1,750

In actual fact the accurate answer would be 1,756 and you can see we were very close.

Example 2

Add 33.90+35.25+34.54+36.21+36.70

If you rounded each of these numbers to the nearest whole number you would have:

34+35+35+36+37

But if you realised the numbers were roughly clustered around 35 i.e.

35+35+35+35+35

5times35 is far easier to work out

5times35=175

In actual fact the accurate answer would be 176.6 and you can see we were very close.

Example 3

Estimate the following calculation:

22times21times18times19

You should recognise that these numbers are clustered around 20

20times20times20times20

which is the same as

2times10times2times10times2times10times2times10

which is the same as

2times2times2times2times10times10times10times10

which is 16times10,000

which is 160,000

NOTE:

The real answer is 158,004