Question

Tommy used benchmark fractions to estimate the sum of 1/5 +3/7 as 1. Tommy's teacher said he was incorrect. Explain what error Tommy might have made and what tips you can give him to solve the problem correctly.

Answer 1

Answer:

Error made by Tommy is he didn't follow the rules of using benchmark fractions to estimate the individual fractions but just added normally and estimated to the highest whole number.

So next time he will have to estimate the individual fractions using the benchmark rules before adding up to get the approximate benchmark sum.

Step-by-step explanation:

A benchmark fraction is used to compare two or more fractions to see if they are lesser than, equal to or greater than the benchmark.

Now, in this question we want to find the benchmark of 1/5 +3/7.

In benchmarks, we have the following rules;

- if the numerator is close to zero, then the fraction is close to zero

-if the numerator is close to half of the denominator, then the fraction is close to ½.

- if the numerator is close to the denominator, then the fraction is close to 1.

Now in our question 1/5 will be closer to zero because the numerator is closer to zero.

But, 3/7 will be closer to ½ because the numerator is close to half of the denominator.

Thus,

1/5 +3/7 will be closer to 0 + ½ = ½

Thus, the correct estimate of the sum using benchmark is ½

Error made by Tommy is he didn't follow the rules of using benchmark fractions to estimate the individual fractions but just added normally and estimated to the highest whole number.

So next time he will have to estimate the individual fractions using the benchmark rules before adding up to get the approximate benchmark sum.