# CLASS-7ROUNDING OFF DECIMAL FRACTION

APPROXIMATION (Rounding Off)

Suppose we want to round off 104, then we have to judge whether it near to 100 or 110. Here 104 is nearest to 100 than 110, so we have to round it off to 100, the rule for rounding off a whole number to the nearest ten is as follows –

If the digit in the one place is less than 5, then we should write zero ‘0’ in the unit place and keep the digits in other places as they are

But, if the digit in the one place is 5 or more than that, then we should write zero ‘0’ in the one place and add 1 to the digit in the tens place.

For better understanding, as per the example –

1) 145 is rounding off to 150 as a digit in the one place is 5 = 5

2) 258 is rounding off to 260 as a digit in the one place is  8 > 5

3) 332 is rounding off to 330 as a digit in the one place is  2 < 5

Rounding off decimal fraction –

Decimal fraction can be rounded off to the nearest one, tenth, hundredth, thousandth, etc. so, to round off a decimal to the nearest unit, remember the following – if the digit in the tenths is less than 5 then we should have write zero ‘0’ in the tenths place and the following decimal places. Keep the other digits as they are.

If the digit in the tenths place is 5 or more than 5, write zeros in the decimal places and increase the digit in the units place by one.

To round off a decimal to the first decimal places, or to the nearest tenths and we should keep in mind, if the digit in the second decimal places is less than 5, we have to write zero ‘0’ in the second and the following decimal places. leave the other digits as they are.

If the digit in the second decimal places is 5 or more than 5, then we should write zero ‘0’ in the second and the following decimal places and add 1 to the digit in the first decimal places.

Example –

1) 2.8 is rounded off to the nearest unit is 3 because 8 > 5

2) 3.2 is rounded off to the nearest unit is 3 because 2 < 5

3) 4.5 is rounded off to the nearest unit is 5 because 5 = 5

4) 12.78 is rounded off to the nearest unit is 13 because 7 > 5

5) 10.31 is rounded off to the nearest unit is 10 because 3 < 5

Significant Figures –

The significant figures of a decimal number are those which must be retained for any position of the decimal point. All non zero digits are significant and so are the zeros between them. We have to start counting from the first nonzero number to the left.

Example –

1)  5.125 kg = 5125 gm

2)  2.25 liter = 225 cl (Centiliter)

3)  4.512 miter = 4512 mm (Millimeter)