Thread: Division revisited.

I have a really stupid question. How do you add fractions, say, 1/2 +1/3 without doing it the long way. Now that I am doing complex fractions, the elementary way doesn't work. Thanks so much!!

JT

Originally Posted by Mathfailure

I have a really stupid question. How do you add fractions, say, 1/2 +1/3 without doing it the long way. Now that I am doing complex fractions, the elementary way doesn't work. Thanks so much!!

JT

What do you call the long way?

Originally Posted by Jhevon

What do you call the long way?

It won't let me write it out, so I'll try to explain it. It's where you take the two fractions, find the LCD, see how many times the dedominator goes into the LCD, times it by the numerator, and finally add the two numerators... If this is confusing you could just show me both ways or all the ways and I'd be more than happy. Thanks

Originally Posted by Mathfailure

1/3 = _6_
24
- - = _1_
1/8 = _3_ 8
24

Ok, so i'm guessing the alignment is off here, i dont get what you're saying.

1/2 + 1/3

obviously the LCM here is 6, so we can do the following:

....1..........1
...---...+...---
....2..........3

....3(1) + 2(1)
= -------------
..........6
.....5
= ----
.....6


OR

....1..........1
...---...+...---
....2..........3

= ....1.....3..........1.....2
......---*---...+...---*---
.......2.....3..........3.....2

......3..........2
=...---...+...---
......6..........6

.....5
= ----
.....6

There is another way still:

you multiply the denominators to get the new denominators, and to get the new numerators, cross multiply opposing numerators and denominators. that is, to get the first numerator, multiply the first numerator in the first original function by the denominator in the second original fraction, then replace the sign, and multiply the second numerator in the second fraction by the denominator of the first fraction, here's a pic:

Originally Posted by Jhevon

There is another way still:

you multiply the denominators to get the new denominators, and to get the new numerators, cross multiply opposing numerators and denominators. that is, to get the first numerator, multiply the first numerator in the first original function by the denominator in the second original fraction, then replace the sign, and multiply the second numerator in the second fraction by the denominator of the first fraction, here's a pic:

Thanks so much! For some reason we only learned the 2nd way that you pointed out back in like 3rd grade.. Thanks again!

Re:

Originally Posted by qbkr21

Re:

what does that -+- in the middle mean?

Its kind of like a code: Multiply the denominators, then just as you stated in your previous post diagonally cross multiply each of the corresponding numerators and denominators