help with fractions?

Question

i have 5/15 + 3/8 and i know that you have to find the lowest common denominator but i forgot please explain?!

Answer 1

Before adding fractions, it is a good idea to reduce each to its lowest terms. That makes the numbers you are working with smaller.
5 divides into 15 three times. You can therefore cancel a 3 from top and bottom of the first fraction, making it 1/3.
The question is now 1/3 + 3/8
Looking at the denominators:
3 is a prime number;
8 = 2*2*2
The LCD is therefore needs to contain three twos and one three multiplied together. This is 2*2*2*3 = 24.
I hope that is enough, and that you can now continue yourself.

Answer 2

yeah you have to first find the lowest common denominator. you have to see what 15 and 8 share.. you do prime factorization to find that.
15 = 3 times 5
8 = 2 (to the power of 3)

so, they don't share anything. Lowest common denominater means you have to multiply the shared and unshared. In this case, you have to multiply 15 by 8 which gives you 120.

you then have to multiply 5 of 5/15 by 8 and 15 by 8 (so that the denominator is equal to 120)
then, multiply 3 of 3/8 by 15 and 8 by 15.

the result: 40/120 + 45/120

add 40 + 45 = 85

the answer = 85/120 (put that it in lowest terms!!!)
final answer = 17/24

Answer 3

1) Factor denominators: 15=3*5, 8=2^3.

2) To find the lowest common denominator (LCD) multiply each factor with the highest power: LCD=2^3*3*5=120.

3) Sum: 5/15+3/8 = [5*(2^3)+3*(3*5)]/120 = (40+45)/120 = 85/120.

Answer 4

just take the common factors of the 2 numbers

15=3 x 5
8=2 x 2 x2
lcd=2x2x2x3x5=120

5/15 =40/120 mulltiply both by 8
3/8= 45/ 120 multiply both by 15

answer 85/120 reduced to 17/24