Question

Which of the following numbers could be used as a common denominator for adding the fractions 2/36 , - 4/35 , and 8/21 ?

(A)105
(B)63
(C)315
(D)7

Answer 1

If i am doing my calculations right the least common denominator is 7

Answer 2

The common denominator for adding the fractions
`(2)/(36)`,
`-(4)/(35)` and
`(8)/(21)` is 1260.

Explanation:

To find : Which of the following numbers could be used as a common denominator for adding the fractions
`(2)/(36)`,
`-(4)/(35)` and
`(8)/(21)` ?

Solution :

To find the common denominator we have to find the least common multiple of 36, 35 and 21

i.e. LCM of 36,35,21

2 | 36 35 21

2 | 18 35 21

3 | 9 35 21

3 | 3 35 7

7 | 1 35 7

5 | 1 5 1

| 1 1 1

`LCM(36,35,21)=2* 2* 3* 3* 5* 7`

`LCM(36,35,21)=1260`

The common denominator for adding the fractions
`(2)/(36)`,
`-(4)/(35)` and
`(8)/(21)` is 1260.