Find the LCM of 4 and 5 (20)
Use that to make equivalent fractions of both terms
3/4 = 15/20
1/5 = 4/20
Use the equivalent terms because now they can be subtracted because they have the same denominator
15/20 - 4/20
=11/20
11 is a prime number, so the fraction cannot be simplified.
First you got to find the Greatest Common Factors or GCF of the denominators or 4 and 5 which is 20. Then, you multiply each side by the number that when multiplied gives you 20 (in this case its each other). 3/4 is now 15/20 and 1/5 is 4/20. Now to add them is quite simple, you're going to add the numerators which gives us a grand total of 15/20+4/20=19/20 in simplest terms.
