27/5 - 32/10 =
54/10 - 32/10 = 22/10 = 11/5 ( you did not make the denominator common.)
Mistake in your 2nd method.
In your first example, when using / for fraction sign you should enclose numerator and denominator in parenthesis.
5*2/5 - 3*2/10=
2 - 3/5 = 10/5 - 3/5 = 7/5
This is the way you have written your problems.
Remember , only fractions with the same denominator can add. So by use of LCM you should make denominators alike, then add, by writing the common denominator and adding the numerator.