## bonjovifan03 2 years ago OK need more help What is 3/8 +5/7? is it 8/15.

1. bonjovifan03

Ty M

That is not correct.

both denominators must be the same.

when we add and subtract they must be the same, multiplying you do not.

5. cwrw238

you must find the lowest common multiple ( LCM of 8 and 7

6. bonjovifan03

so would it be 1/7?

7. cwrw238

you can only add the top numbers when the denominator is the same

nope that isn't correct.

9. cwrw238

LCM = 7*8 = 56

Lets find the LCD(Least Common Denominator) HINT: If we cannot find a number lower, we usually multiply the bottom numbers, so in this case 7*8 =?

cwrw trying to steal my Q!

12. cwrw238

now you need to convert 3/8 to something over 56

13. bonjovifan03

so 61/56 ? Im lost

correct.

15. cwrw238

ok - sorry - you carry on

:p

17. bonjovifan03

ty all

Do you undertstand how you got that answer though?

19. bonjovifan03

Yes and no? 56yes but no to sure on the 61

20. bonjovifan03

So if you divide 25/6 by 5 is it 5/6?

21. bonjovifan03

ty

well actually I wouldn't say that.

normally the trick when you have multiple denoms you do this. A/B/C = A *C/B

Sorry I said yes, when I was checking my answer it seemed to give me that, and the other one I thought.

So 25 / 6 / 5 would be 25 * 5/6

26. bonjovifan03

so would it be 25/30?

What is 25*5

28. bonjovifan03

125

/6

30. bonjovifan03

so 125/6?

yes.

http://www.wolframalpha.com/input/?i=%2825%29%2F%286%2F5%29 Depending how you put it into Wolfram you could get 5/6, though I'm not 100% sure why..

@jim_thompson5910

34. bonjovifan03

OK ty

35. jim_thompson5910

3/8 + 5/7 (7/7)*(3/8) +5/7 21/56 +5/7 21/56 + (5/7)*(8/8) 21/56 + 40/56 (21+40)/56 61/56 So 3/8 + 5/7 = 61/56