To add or subtract rational numbers in fractional form?

Question

7/8 plus 5/6 = 21/24 plus 20/24 I understand that 24 is the LCM, but I don't understand how they got the numerator. Please explain.

Answer 1

you understand that the lcm is 24 because they both have 24 as a multiple. You also must remember what each denominator was multiplied by. the 8 was multiplied by 3 and the 6 by 4. whatever you multiply the denominator by to get the lcm you must also multiply the numerator. so 3 times 7 is 21 and 4 times 5 is 20. I hope this helps.

Answer 2

7/8(3/3)=21/24 5/6(4/4)=20/24 Once you determine LCM you multiply numerator/denominator by number to achieve LCM. All you are doing is multiplying by one. Hope this helped.

Answer 3

The LCM is 24(LCD)

7/8+5/6=
24/8=3
A math rule is whatever you do the denominator you do to the numerator
7/8 x 3/3=21/24

5/6
24/6=4
5/6 x 4/4=20/24
21/24+20/24=41/24=1 17/24

Another way to do it would be tocross multiply

7/8=x/24
8x=168
8/8x=168/8
x=21

5/6=x/24
6x=120
6x/6=120/6
x=20

21/21+20/24=41/24= 1 17/24

Answer 4

the lcm is 24 so what is the denominator multipled by to make the 24??? well for 8 its going to be 8*3 so you multiple the numerator by 3 also so it should be

(7*3)/(8*3) that equals 21/24

for 6 its going to be 4 so

(5*4)/(6*4) that equals 20/24

Answer 5

24/8=3 so you multiply 7 by 3 to get 21.
24/6=4 so you multiply 5 by 4 to get 20.

Answer 6

7/8 x 3/3 = 21/24
5/6 x 4/4 = 20/24