Page 59 - Maths Class 05

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After calculating the least common multiple, always check to be sure that the answer can
be divided by both the numbers without leaving a remainder.

LCM of given numbers can be found by anyone of the following methods :

« By Multiple Method « By Prime Factorisation Method

« By Division Method

LCM by Multiple Method

This method works best when you are working with two numbers that are less than 10.

If you are working with larger numbers, it's best to use a different method.

Example : Find the least common multiple of 5 and 8.

Solution : Since, these are small numbers, it is appropriate to
use this method. Write the first several multiples of

the first number 5. The first several multiples of 5

are 5, 10, 15, 20, 25, 30, 35 and 40.

5 : 5, 10, 15, 20, 25, 30, 35, 40

Write the first several multiples of the second number 8.
The first several multiples of 8 are 8, 16, 24, 32, 40, 48, 56

and 64. Do this near the first set of multiples, so that they

are easy to compare.

Find the smallest multiple that both the numbers have in common. You

might need to extend your list of multiples until you find one common
multiple. This number will be your least common multiple.

5 : 5, 10, 15, 20, 25, 30, 35, 40

8 : 8, 16, 24, 32, 40 , 48, 56, 64
LCM = 40

The smallest multiple that 5 and 8 have in common is 40. So, the least

common multiple of 5 and 8 is 40.

Mathematics-5 59