# Help with a pre-algebra question

• Oct 13th 2007, 05:17 PM
Jason29
Help with a pre-algebra question

Simplify:

28 - 9 and 21/35

I got 9 and 3/5 as my answer.
• Oct 13th 2007, 05:29 PM
Ben Tillman
For this one: 28 - 9

If the problem was 28 - 8, would you agree with me that the answer would be 20? So now if I take one more away, that is 28 - 9, I should have 19 right?

When simplifying ones like 21/35, see if you can see a common factor in the numerator and denominator. I see a 7 (maybe there are more, but we can deal with them one at a time), that is,

$\displaystyle \frac{21}{35} = \frac{7 \times 3}{7 \times 5}.$

Now, you should be able to convince yourself that 7/7 = 1. So our fraction becomes

$\displaystyle \frac{7 \times 3}{7 \times 5} = 1 \times \frac{3}{5} = \frac{3}{5}.$

So your second answer looks good. As an additional note, since 3 and 5 are both prime numbers, we can instantly say this can not be simplified any further.

Hope that helps.
• Oct 13th 2007, 05:38 PM
Jason29
thanks
• Oct 13th 2007, 11:31 PM
~V~
9 and 3/5
Working this problem out, I do not get 9 3/5 as an answer. I'm in the same class as Jason29 though, so I could be way off base here. Anyway, the answer I keep coming up with is 18 2/5. :confused:

Anybody else have input on this problem?

Uh oh,
~V~
• Oct 13th 2007, 11:43 PM
Jhevon
Quote:

Originally Posted by ~V~
Working this problem out, I do not get 9 3/5 as an answer. I'm in the same class as Jason29 though, so I could be way off base here. Anyway, the answer I keep coming up with is 18 2/5. :confused:

Anybody else have input on this problem?

Uh oh,
~V~

if the problem is $\displaystyle 28 - 9 \frac {21}{35}$

then you are correct. the answer is $\displaystyle 18 \frac 25$ or, as i would prefer to write, $\displaystyle \frac {92}5$, but for some reason, writing improper fractions is a sin at this level, i think they are neater
• Oct 13th 2007, 11:49 PM
~V~
Jhevon~
Phew! Thanks for your input! This quiz was already submitted, but now I know the answer I gave is correct.
Relieved(Whew),
~V~
• Oct 13th 2007, 11:52 PM
Jason29
I just tried the problem again and this time I got the same answer as V. Thanks for keeping me honest!!!
• Oct 14th 2007, 12:04 AM
Jhevon
Quote:

Originally Posted by Jason29
I just tried the problem again and this time I got the same answer as V. Thanks for keeping me honest!!!

that's ok. just be clearer with your question next time. obviously Ben Tillman thought you were asking something else, and even i was wondering what you were talking about for a while
• Oct 14th 2007, 12:09 AM
Ben Tillman
Oops. Sorry, I thought you were asking two separate questions.
• Oct 14th 2007, 12:12 AM
Jhevon
Quote:

Originally Posted by Ben Tillman
Oops. Sorry, I thought you were asking two separate questions.

i thought so at first myself, then i realized that there is no way he could have gotten 9 for the first answer
• Oct 14th 2007, 12:18 AM
Ben Tillman
Actually I thought it was a typo (dropped the 1), so I just went through it anyway.

Sorry again!