Page 31 - Viva

Example 6: Add 232, 453 and 172 using the expanded form.

Solution: H T O Expanded form H T O

2 3 2 200 + 30 + 2 7 0 0
4 5 3 400 + 50 + 3 1 5 0

+ 1 7 2 + 100 + 70 + 2 + 7

700 + 150 + 7 8 5 7

So, 232 + 453 + 172 = 857.

Estimating the Sum
Estimation gives a rough (or approximate) value of the sum. We can round off a number
to any place depending upon the degree of accuracy required.

To estimate the sum, round off the given addends to the nearest 10, 100, 1000, etc., and
then add.

Example 7: Estimate the following sums by rounding off the addends as mentioned.

(a) 456 + 231 + 20 (to the nearest ten)
(b) 484 + 258 + 140 (to the nearest hundred)

Solution: (a) 456 + 231 + 20

= 460 + 230 + 20 (rounding off each addend to the nearest 10)

= 710
(b) 484 + 258 + 140

= 500 + 300 + 100 (rounding off each addend to the nearest 100)

= 900

Example 8: A box contains 45 red balls, 78 blue balls and 98 green balls. Calculate the
number of balls in the box using estimation method by rounding off each
number to the nearest 10. Check whether the estimated sum is close to the
actual sum or not.

Solution: Approximate number of red balls = 5 0 (45 is rounded off to 50)

Approximate number of blue balls = 8 0 (78 is rounded off to 80)

Approximate number of green balls = + 1 0 0 (98 is rounded off to 100)
Total number of balls in the box = 2 3 0 (estimated value)

So, there are approximately 230 balls in the box.

Now let’s find the actual number of balls in the box.

21