Emil used 3/4 of a red bottle of paint and 1/5 of a blue bottle of paint in art class. how much paint did he use in all?

First change the fraction to decimals or common denominators.
3/4 = 0.75 and 1/5 = 0.2
0.75 + 0.2 = 0.95 = 95/100 = 19/20

(3/4) = (15/20)
(1/5) = (4/20)
(15/20) + (4/20) = 19/20

3/4+1/5=19/20
Multiply 4 by 5 to get a LCD and 20 will be your new denominator,
Multiply the 3 by 5 and put that as the numerator of the new first fraction
(3/4)*5/5=15/20
Multiply the 5 by 4 to get 20 and that will be the denominator of the second fraction, the multiply 1 by 4 and put that over the denominator,
(1/5)*4/4=4/20
Now you can just add across,
15/20+4/20=19/20.