Question

A student estimated the sum

7.95 + 8.11 + 78.5 + 8.05 + 79.4 + 0.815 as:

All the numbers begin with a 7 or 8, so use cluster estimation.
8 + 8 + 80 + 8 + 80 + 0.8 = 184.8

Explain why this reasoning is not accurate.

Answer 1

cluster estimation - "Cluster estimation can be used to estimate sums and products when the numbers you are adding or multiplying cluster near or is close in value to a single number."

so when all are close to a single number, if all numbers begin with a 7 or 8 means nothing,' for example you have 78.5 and .815
one is like close to the hundreds and one is like less than 1, these are not close to each other and therefore this reasoning is not accurate