Page 44 - Maths Class 05

Example : The school cook prepared lunch for 186 boys and 212 girls. Estimate the

total number of students for whom the school cook prepared lunch.

Solution : To estimate the total number of students who get lunch, we round off the
number of boys and girls to the nearest ten or hundred and add :

Rounding off to nearest 10 Rounding off to nearest 100

Actual Sum Estimated Sum Actual Sum Estimated Sum

1 8 6 1 9 0 1 8 6 2 0 0

+ 2 1 2 + 2 1 0 + 2 1 2 + 2 0 0
3 9 8 4 0 0 3 9 8 4 0 0

Estimating Differences

Example : Estimate the following to the nearest hundred by showing actual difference :

a. b.
4 5 7 7 3 9
– 2 4 6 – 4 7 9

Solution : a. Actual Difference Estimated Difference
Rounding
4 5 7 off to the 5 0 0
Nearest
– 2 4 6 – 2 0 0
100
2 1 1 Nearest 3 0 0
100

We get that the actual difference differs by 89 from estimated difference.

b. Actual Difference Estimated Difference
Rounding
7 3 9 off to the 7 0 0
Nearest
– 4 7 9 – 5 0 0
100
2 6 0 Nearest 2 0 0
100

We get that the estimated difference differs by 60 from actual difference.

Estimating Products and Quotients

Example : Estimate the product of 42 and 48 to the nearest ten.

Solution : Rounding off
42 to the Nearest 40
Hence, estimated product of 42 and 48
10
48 Nearest 50 = 40 × 50 = 2000
10

Mathematics-5 44