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
5×350 is far easier to work out
5×350=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
5×35 is far easier to work out
5×35=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:
22×21×18×19
You should recognise that these numbers are clustered around 20
20×20×20×20
which is the same as
2×10×2×10×2×10×2×10
which is the same as
2×2×2×2×10×10×10×10
which is 16×10,000
which is 160,000
NOTE:
The real answer is 158,004
