What is -4/5 + 3/20 in simplest form

-4/5 = -16/20, so the new expression is (-16/20)+(3/20)
then, -16 + 3 is -13, so the solution is -13/20

-4/5 + 3/20 = 3/20 - 4/5

To subtract 2 fractions, they both need to have the same denominator.
Since 5 is one of the divisors of 20, we can just multiply the numerator and denominator of 4/5 by 4.
4/5 = (4*4) / (5*4) = 16/20

P.S. when the denominators of both fractions don't have any relation, you multiply the numerator and denominator of the first fraction by the denominator of the second, and the numerator and denominator of the second by the denominator of the first.

3/20 - 4/5 = 3/20 - 16/20

Now you just subtract the numerators:
3/20 - 16/20 = (3-16)/20 = -13/20

So -4/5 + 3/20 = -13/20

Hope this helps! :)