What is three eighths plus three fourths?

Answer 1

3/8 + 3/4:

Make them fractions with the same denominator (in this case eighths):

3/4 = 6/8

Now they can be added and simplified:

3/8 + 3/4 = 3/8 + 6/8

= 9/8

= 11/8

There is a "trick" that works for adding or subtracting any two fractions:

a/b ± c/d = (ad ± cb)/bd

That is

1. multiply the top number of the first fraction (a) by the bottom number of the second fraction (d) then;
2. add/subtract the top number of the second fraction (c) multiplied by the bottom number of the first fraction (b) and finally;
3. put the result (of step 2) as the top number over the two bottom numbers (b and d) multiplied together.

(Note that this can result in extra work when simplifying the result.)

Examples:

5/8 + 3/4 = (5x4 + 3x8)/8x4

= (20 + 24)/32

= 44/32

= 11/8

= 13/8

4/5 - 3/7 = (4x7 - 3x5)/5x7

= (28 - 15)/35

= 13/35