Everything Maths Grade 10

Worked example 4: Rounding off

QUESTION

Round off the following numbers to the indicated number of decimal places:

1.

120

99

=1, 1 _ 2 _to 3 decimal places.

2.=3,141592653... to 4 decimal places.

3.

p

3 =1,7320508... to 4 decimal places.

4.2,78974526 to 3 decimal places.

SOLUTION

Step 1: Mark off the required number of decimal places

If the number is not a decimal you first need to write the number as a decimal.

1.

120

99

=1,212j 121212 : : :

2.=3,1415j 92653 : : :

3.

p

3 =1,7320j 508 : : :

4.2,789j 74526

Step 2: Check the next digit to see if you must round up or round down

1.The last digit of^12099 =1,212j 1212121 _ 2 _must be rounded down.

2.The last digit of=3,1415j 92653 : : :must be rounded up.

3.The last digit of

p

3 =1,7320j 508 : : :must be rounded up.

4.The last digit of 2,789j 74526 must be rounded up.

Since this is a 9 we replace it with a 0 and round up the second last digit.

Step 3: Write the final answer

1.

120

99

=1,212 rounded to 3 decimal places.

2.=3,1416 rounded to 4 decimal places.

3.

p

3 =1,7321 rounded to 4 decimal places.

4.2,790

Exercise 1 – 2:

1.Round off the following to 3 decimal places:

a) 12,56637061... b)3,31662479... c) 0,2666666...

d)1,912931183... e)6,32455532... f) 0,05555555...

2.Round off each of the following to the indicated number of decimal places:

a)345,04399906 to 4 decimal places.

b)1361,72980445 to 2 decimal places.

c)728,00905239 to 6 decimal places.

Chapter 1. Algebraic expressions 13