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Example 2. A shopkeeper had 662 balls. He sold 245 balls. Estimate the number of
unsold balls by rounding to the nearest 10. Is the number of balls left unsold more
than 400 or less than 400?
Solution. Actual difference Estimated difference

6 6 2 round off 6 6 0
– 2 4 5 round off – 2 5 0

4 1 7 4 1 0

Thus, the shopkeeper has more than 400 balls left unsold with him.

21 st
Activity Century #Experiential Learning
Skills

Subtraction race to Zero or any other target number
Play with your partner. Choose any 3- or 4-digit number and write it on a sheet of paper.
For example: 1000
One player starts the game. He/she takes 2-3 dice and rolls them. Using the numbers
face up, form a 2- or 3-digit number.
Round off the number to the nearest 10 and then subtract it from
your chosen number.
Number formed = 326 and rounded off to 330
Then, 1000 – 330 = 670.

Similarly, the other player will take a turn and do the same process.
Then, the first player will repeat the process to get the next number and subtract it from
the number obtained in the previous step.
Continue the activity until one player reaches the number 0. The player who reaches the
target number, wins the game.

Exercise 3E

First, find the actual difference. then, find the estimated difference by rounding to the
nearest 10. Finally, compare both the results.
1. 87 – 23 2. 167 – 94

Actual Estimated Actual Estimated

8 7 1 6 7
– 2 3 – – 9 4 –

64 Mathematics 3