How do you know if the sum or difference in an equation involving

fractions is reasonable? For example:

+ =

In this lesson you will learn how to determine the

reasonableness of sums and differences using benchmark

fractions.

Let’s Review

Numerator: The number of parts

being considered

Denominator:

The number of equal parts in the whole

13

Let’s Review

0 1

Benchmark Fractions

whole

parts

0

1

Let’s Review

Estimating with whole numbers

Students in the craft club made 48 white paper snowflakes and 54 glittery silver icicles for the winter ball. How many decorations did they prepare in all?

Both numbers are close to 50.

50 + 50 = 100 100101000about

Core Lesson

0 1

Estimating with fractions

is closest to 0 is closest to 1

Rounding to the nearest half

Core Lesson

There are two main uses for rounding fractions to the nearest half

Rounding fractions to estimate sums and differences1

2 Rounding fractions to determine reasonableness of sums and differences

∙ when exact answers are not needed∙ before calculations

∙ during or after calculations

Core Lesson

0 1

Rounding fractions to estimate sums and differences

0 1+ + =1= 1about

1

Core Lesson

Sophia’s hermit crab eats of a cup of rice and of a cup of fruit per week.

+ = 0 + =about

Core Lesson

0 1

Rounding fractions to determine reasonableness of sums and differences

1- - ==

2

Core LessonTyler mowed of the lawn on Monday and

of the lawn on Tuesday. His father said that he mowed of the lawn in all.

+ = aboutx

In this lesson you have learned how to determine

the reasonableness of sums and differences using benchmark fractions.