Addition of Fractions by Two Different Methods that Don't Agree?

Question

We can add fractions by mainly 2 methods (atleast I know only two).

1.LCD

2.LCM

I will add two different fractions by both the methods.

Fraction is:

1/36 + 1/27

By LCM

Dividing the denominator by 9.

We get,

1/4 + 1/3

Cross multiplying

3+4/ Lcm of 36 & 27

ie;

7/108.

Now By LCD

1×27/36×27 + 1×36/27×36

This gives,

63/972 = 7/108

Other Fraction is:

5/6+1/15

By LCM

Dividing denominator by 3

we get

5/2 + 1/5

Cross multiplying

25+2/ LCM of 6 & 15

ie;

27/90 = 0.3

By LCD

5×15/6×15 + 1×6/15×6

This will be

75+6/90= 81/90 = 0.9

Here in second fraction, I am getting two different answers.

Please, tell where I am going wrong. Is my method of solving by LCM in second fraction wrong? This question seems to be childish, I know.Since I don't have any mentor to ask I am compelled to ask here. But please help! I am still learning.

Thank you

Answer 1

1/4 + 1/3

Cross multiplying

3+4/ Lcm of 36 & 27

ie;

7/108

This is not correct. Note that 1/4 and 1/3 are each way bigger than 7/108.