How do I figure out 7-7/8 x 2-4/7?

Question

I'm getting the answer 20-7/28. Not sure if I got to this answer right. I am converting 7-7/8 and 2-4/7 into improper fractions - I get 63/8 and 18/7, respectively. Then I solved 63/8 x 18/7 which came to 567/28 = 20-7/28. What am I doing wrong here???

Answer 1

Right, except that you forgot the simplify the answer. 7 and 28 are both divisible by 7, so 7/28 reduces to 1/4.

Here's a trick that can make this kind of problem easier. When you are multiplying a fraction times a fraction, you can reduce any numerator with any denomiator, which gives you smaller numbers to work with.

So, when you have 63/8 times 18/7, you can reduce the 63 and the 7, and you can reduce the 8 and the 18.

This gives you 9/4 times 9/1, or 81/4, which becomes 20 1/4.

Answer 2

7 7/8 x 2 4/7=

63/8 x 18/7=81/4=20 1/4

Answer 3

( 7 - 7/8 ) X (2 - 4/7) = 6,1/8 X ( 2 - 4/7)
= 6,1/8 X 1, 3/7
= 49/8 X 10/7

= 49/4 X 5/7
= 7/4 X 5/1
= 35/4
= 8,2/4
= 8,1/2 (correct answer)

What you do is...calculate the ones in brackets first. Then make them into improper fractions... Cross divide them.
For example,

49 , 10
______

8 , 7

You take 8 and 10 to cross divide. 8 / 2 = 4 . 10 / 2 = 5.
Then you take 49 and 7 to cross divide. 49 / 7 = 7. 7 / 7 = 1.
So you will get...7/4 X 5 = 35/4 = 8,1/2.

Answer 4

(63/8)(18/7) =

63 X 18
_______
8 X 7


9 X 7 X 2 X 3 X 3
_______________
2 X 4 X 7


9 X 9
_____ (when divided by common factors 7 and 2) = 81 / 4
4

Answer 5

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