Page 37 - Start Up Mathematics_4

Estimating the sum means rounding off the given numbers to the nearest 10; 100; 1,000,
etc. and then adding the numbers obtained.

Example 9: A box contains 2,645 red balls, 1,378 blue balls and 1,798 green balls. How
many balls are there in the box? Calculate using estimation method by

rounding off to the nearest 100. Check whether the estimated sum is close
to the actual sum or not.
1
Solution: Number of red balls (rounded off) = 2 6 0 0
Number of blue balls (rounded off) = 1 4 0 0

Number of green balls (rounded off) = + 1 8 0 0
Total balls in the box = 5 8 0 0

There are approximately 5,800 balls in the box.

Let’s now find the actual number of balls in the box.

1 2 2
Red balls = 2 6 4 5
Blue balls = 1 3 7 8

Green balls = + 1 7 9 8
Total balls = 5 8 2 1

5,821 when rounded off to the nearest 100 gives 5,800.

So, the estimated number of balls is very close to the actual number of balls
in the box.

Solving Word Problems

Example 10: A publisher sold 46,750 books in the month of January; 1,52,430 books in the
month of February and 1,60,000 books in the month of March. How many
books did the publisher sell in 3 months?

L TTh Th H T O

Solution: Number of books sold in January = 1 4 1 6 7 5 0

Number of books sold in February = 1 5 2 4 3 0

Number of books sold in March = + 1 6 0 0 0 0

Total number of books sold = 3 5 9 1 8 0

So, the publisher sold 3,59,180 books in 3 months.

Example 11: The population of a small town in the year 2011 was 2,35,170. In the next year,
the population of the town increased by 62,000. What was the population in
the year 2012?

29