Discussion about math, puzzles, games and fun. Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ π -¹ ² ³ °

You are not logged in.

- Topics: Active | Unanswered

- Index
- » Exercises
- »
**Proportion**

Pages: **1**

**Al-Allo****Member**- Registered: 2012-08-23
- Posts: 299

I just have a little problem :

X 8

_= _

7 9

If I would want to solve for X, I would multiply by 7 for each side. Leaving x=56

___

9

But what I did is x=56

__

63

Could somebody explain me why it's wrong ?

Thanks

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 92,880

When you multiply by 7 you cancel the 7 on the left but not the 9 on bottom right.

Correct thing to do is to cross multiply

9x = 56

x = 56 / 9

**In mathematics, you don't understand things. You just get used to them.**

**I agree with you regarding the satisfaction and importance of actually computing some numbers. I can't tell you how often I see time and money wasted because someone didn't bother to run the numbers.**

Offline

**Al-Allo****Member**- Registered: 2012-08-23
- Posts: 299

But I mean not canceling the 9 but multiplying it by 7, it's not a right thing to do ? Thanks

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 92,880

If you multiply by 7 you are going to get:

x = 56 / 9 which is the same thing.

**In mathematics, you don't understand things. You just get used to them.**

**I agree with you regarding the satisfaction and importance of actually computing some numbers. I can't tell you how often I see time and money wasted because someone didn't bother to run the numbers.**

Offline

**Al-Allo****Member**- Registered: 2012-08-23
- Posts: 299

bobbym wrote:

If you multiply by 7 you are going to get:

x = 56 / 9 which is the same thing.

ok, I understood. Thanks

*Last edited by Al-Allo (2013-02-02 07:30:14)*

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 92,880

Hi;

You are welcome.

**In mathematics, you don't understand things. You just get used to them.**

**I agree with you regarding the satisfaction and importance of actually computing some numbers. I can't tell you how often I see time and money wasted because someone didn't bother to run the numbers.**

Offline

Pages: **1**

- Index
- » Exercises
- »
**Proportion**