Page 124 - Start Up Mathematics_1

11 Subtract mentally.

(a) 58 – 5 = (b) 39 – 30 =

(c) 79 – 3 = (d) 67 – 24 =

(e) 42 – 2 = (f) 83 – 22 =

Subtraction on a Number Line

We already know that subtraction on a number line means counting backward.

Look at the example, 24 – 7 = ?

Starting from 24, subtract 7 by counting backward and you will reach 17.

So, 24 – 7 = 17

16 17 18 19 20 21 22 23 24 25

Alternate Method

Step 1: Draw a line and write back at the right end.
back

Step 2: Write 24 below the back mark.

back

24

Step 3: Mark 7 sticks at equal distance and count backward to get the answer.

back

17 18 19 20 21 22 23 24
So, 24 – 7 = 17

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