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
Example # 1:
Estimate 699 + 710 + 695 + 705 + 694 + 715
Carefully examine all the numbers above. You should notice that they all cluster around 700
Therefore, 700 + 700 + 700 + 700 + 700 + 700 will give us a good estimate for the answer.
Instead of adding 700 six times, just do 6 × 700.
700 × 6 = 4,200 is a good estimate of the sum
In fact, the real answer 699 + 710 + 695 + 705 + 694 + 715 = 4,218. Thus 4,200 is indeed close to the real answer
Example # 2:
Estimate 257 + 247 + 255 + 245
Carefully examine all the numbers above. You should notice that they all cluster around 250
Therefore, 250 + 250 + 250 + 250 will give us a good estimate for the answer.
Instead of adding 250 four times, just do 4 × 250.
250 × 4 = 1,000 is a good estimate of the sum
In fact, 257 + 247 + 255 + 245 = 1004. Thus 1000 is indeed close to the real answer
Example # 3:
Estimate 23 × 18 × 22 × 17
This time, you are estimating a multiplication problem. However,you will still use cluster estimation to estimate the product.
Just notice that all numbers above cluster around 20
Therefore, 20 × 20 × 20 × 20 will give us a good estimate for the answer.
Multiply the 2s to get 16.
Then, just put four zeros after 16 to get 160,000
The real answer is 23 × 18 × 22 × 17 = 154,836.
It is not a very good estimate, but we can live with that
In general, addition will give better estimates
Example # 4:
Estimate 8 × 11 × 12
Just notice that all numbers above cluster around 10
Therefore, 10 × 10 × 10 will give us a good estimate for the answer.
10 × 10 × 10 = 1000
The real answer is 8 × 11 × 12 = 1056.

Feb 02, 18 05:18 PM
These preschool math worksheets will help kids prepare for kindergarten math
Read More
New math lessons
Your email is safe with us. We will only use it to inform you about new math lessons.