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subtraction of a number from itself Estimating DiffErEncE

When a number is subtracted from itself, we get 0 as the difference. Like addition, we can also estimate the difference by rounding off.
Examples: (a) 26 – 26 = 0 (b) 324 – 324 = 0 (c) 1248 – 1248 = 0 Example 1: Estimate the difference of 64 and 87 by
rounding them to the nearest 10. Then, compare it Think Tank
subtracting 10, 100 anD 1000 with their actual difference. Neha is decorating her school

subtracting 10 from a number Solution: Actual difference Estimated difference with about 100 diyas on the
occasion of Diwali. She bought
T O T O 24 diyas and her teacher gave
When we subtract 10 from a given number, we subtract 1 from the digit at the tens place 8 7 rounded up 9 0 her 38 diyas. Give a rough

and the ones digit remains the same. – 6 4 rounded down – 6 0 estimate of how many more

Examples: (a) 57 – 10 = 47 (b) 493 – 10 = 483 (c) 1619 – 10 = 1609 2 3 3 0 diyas she should buy.
The estimated difference is greater than the actual difference.

subtracting 100 from a number Example 2: A shopkeeper had 662 balls. He sold 245 balls. Estimate the number of unsold
When we subtract 100 from a given number, we subtract 1 from the digit at the hundreds balls by rounding off to the nearest 10. Is the number of unsold balls more than or less

place and the tens and ones digits remain the same. than 400?

Examples: (a) 295 – 100 = 195 (b) 587 – 100 = 487 (c) 2699 – 100 = 2599 Solution: Actual difference Estimated difference
H T O H T O
subtracting 1000 from a number 6 6 2 rounded down 6 6 0

When we subtract 1000 from a given number, we subtract 1 from the digit at the – 2 4 5 rounded up – 2 5 0
4
1
1
7
0
4
thousands place and the hundreds, tens and ones digits remain the same.
Examples: (a) 9397 – 1000 = 8397 (b) 2695 – 1000 = 1695 The estimated number of unsold balls is 410.
Clearly, the shopkeeper has more than 400 unsold balls.
Think Tank Critical Thinking Practice time 3D
1. If 1000 – 9 = 991, then what is 9000 – 9? Find the estimated difference by rounding to the nearest 10. Then find the actual
2. What is the difference between 723 tens and 7 thousands 23 tens? difference and compare.

1. Actual difference Estimated difference 2. Actual difference Estimated difference

Practice time 3c T O round off T O T O T O
8 7 9 4 round off
1. Fill in the blanks using subtraction properties. – 2 3 round off – – 6 5 round off –

(a) 273 – 0 = ______ (b) 564 – ______ = 564 (c) 7364 – 0 = ______

(d) 575 – 1 = ______ (e) 649 – ______ = 648 (f) ______ – 1 = 276 3. Actual difference Estimated difference 4. Actual difference Estimated difference
H T O H T O H T O H T O
2. Subtract the following.
1 6 7 round off 2 6 4 round off
(a) 425 – 10 (b) 896 – 10 (c) 567 – 100 – 9 4 round off – – 1 8 5 round off –

(d) 4364 – 100 (e) 2645 – 1000 (f) 5730 – 1000

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