Category : 4th Class

Synopsis

• When two numbers are added, each of them is called an addend and the answer obtained is called the sum.

e.g.,

• Two numbers added in any order give the same sum.

e.g., 4126+3143 =7269

Also, 3143+4126 =7269

• When one of the addends is 0, the sum is the addend other than 0.

e.g., 6740 + 0 = 6740

In other words, when zero (0) is added to any number, the sum obtained is the number itself.

• When two numbers are added (none of them is zero), their sum is greater than each of the numbers.

e.g., 5365 + 2234 = 7599

7599 > 5365 and 7599 > 2234

The addends can be estimated to the nearest 1000 or 100.

(a) Estimating to the nearest 1000:

• rounds to 3000.
• 6215 rounds to 6000.

So, 3000+6000 =9000

Actual sum = 3451 + 6215 = 9666

(b) Estimating to the nearest 100:

3451 rounds to 3500.

9700 is closer to the actual sum i.e., 9666 than 9000.

So, rounding a 4-digit addend to the nearest 100 gives a better estimate of the sum.

1. Subtraction:

• The answer obtained when two numbers are subtracted is called difference. The number which is subtracted is called the subtrahend and the number from which another number is subtracted is called the minuend.

e.g.,

 62135 - 30014 = 32121 Minuend Subtrahend Difference

Properties of subtraction:

(a) While subtracting, the order in which numbers are taken is important.

e.g., 4261 - 3417 is not the same as 3417 - 4261.

Note: Only smaller number can be subtracted from the larger ones.

(b) When '0' is subtracted from a number/the difference is the number itself.

(c) On adding the difference and the subtrahend, we get the minuend.

(d) The difference of two numbers is always lesser than the minuend.

(e) When a number is subtracted from itself, the difference is zero.

Subtraction (using estimation):

e.g., Subtract 3451 from 6215.

The subtrahend and the minuend can be estimated to the nearest 1000 or 100.

(a) Estimating to the nearest thousand:

3451 rounds to 3000.

6215 rounds to 6000.

So,

(b) Estimating to the nearest hundred:

3451 rounds to 3500.

6215 rounds to 6200.

So,

Actual difference

2700 is closer to the actual difference i.e., 2764 than 3000.

So, rounding to the nearest hundred gives a better estimate of the difference.

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