Page 106 - Start Up Mathematics_5

Multiplication with whole numbers

Rahul goes to a stationery shop to buy
pencils.

Rahul : Uncle, how much are
these pencils for?
Shopkeeper : ` 3.25 each.

Rahul : I need four. So the total
would be? Hmm…
` 13.00.

That was easy for Rahul. Now let’s see how he calculated this figure following these steps.
Step 1: Ignore the decimal point and multiply like any two whole numbers. 1 2

Step 2: Count the digits after the decimal point in the decimal number 3 2 5
3.25. × 4

Step 3: Starting from the extreme right of the product, move towards left 1 3 0 0
counting the number of digits obtained in step 2 and place the 13 . 00
decimal point.

Example 7: Find the product of 52.65 and 17.

1 4 3
Solution: 5 2 6 5 Try These!
× 1 7
(a) 68.7 × 9
1 1
3 6 8 5 5 (b) 91.23 × 12
+ 5 2 6 5 0 (c) 124.95 × 17
8 9 5 0 5

So, 52.65 × 17 = 895.05

Multiplication of two decimal numbers

To multiply any two decimal numbers, we follow these steps.

Step 1: Ignore the decimal points and multiply as whole Try These!
numbers.

Step 2: Count the digits after the decimal point in both the (a) 3.40 × 1.5
numbers. (b) 5.25 × 3.4
(c) 7.07 × 2.3
Step 3: Starting from the extreme right of the product,
move towards left counting the number of digits
obtained in step 2 and place the decimal point.

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