Page 20 - WCS - Electrical

3 2 5 6 WORKSHOP CALCULATION & SCIENCE - CITS
(1 X 10) + (2 X 1) + + + +
10 100 1000 10000

5 35 127 3648
Ex. = 0.5, = 0.35 = 0.0127, = 3.648
10 100 10000 1000
Addition and subtraction

0.25
0.75
Arrange the decimal fractions in a vertical order, placing the decimal point of each fraction to be added or
75
100
0.75
subtracted, in succession one below the other, so that all the decimal points are arranged in a straight line. Add
x
=
100
0.25
25
or subtract as you would do for a whole number and place the decimal point in the answer below the column of
decimal points. 3
75 =
25
Decimal fractions less than 1 are written with a zero before the decimal point. Example: 45/100 = 0.45 (and not
simply .45)
900
Add 0.375 + 3.686
72.79
0.375
3.686
4.061
Subtract 18.72 from 22.61
22.61
18.72
3.89
Multiplication
Ignore the decimal points and multiply as whole numbers. Find the total number of digits to the right of the
decimal point. Insert the decimal point in the answer such that the number of digits to the right of the decimal
point equals to the sum of the digits found to the right of the decimal points in the problem.
Multiply 2.5 by 1.25

= 25 x 125 = 3125. The sum of the figures to the right of decimal point is 3. Hence the answer is 3.125.
3
5
6
2
(1 X 10) + (2 X 1) + + + +
Division
10 100 1000 10000
Move the decimal point of the divisor to the right to make it a full number. Move the decimal point in the dividend
5 to the same number of places, adding zeroes if necessary. Then divide.
3648
127
35
Ex. = 0.5, = 0.35 = 0.0127, = 3.648
10000
100
10 Divide 0.75 by 0.25 1000
0.25 0.75
0.75 x 100 = 75
0.25 100 25
25 75 = 3
Move the decimal point in the multiplicand to the right to one place if the multiplier is 10, and to two
900
places if the multiplier is 100 and so on. When dividing by 10 move the decimal point one place to
72.79
the left, and, if it is by 100, move them point by two places and so on.
Example
Allowance allowing 3 mm for cutting off each pin, how many pins can be made from a 900 mm long bar and how
much material will be left out?

7

CITS : WCS - Electrical - Exercise 1 CITS : WCS - Electrical - Exercise 1