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**bronxsystem****Member**- Registered: 2013-06-22
- Posts: 63

basic algebra but im having trouble with it

any advice much appreciated

The sum of two numbers is 23. Seven times the first number less five times the second number is equal to 5. What are the two numbers?

not sure where to start ><

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 87,200

a + b = 23

7a - 5b = 5

The first number is 10 and the second number is 13.

Welcome to the forum.

**In mathematics, you don't understand things. You just get used to them.Of course that result can be rigorously obtained, but who cares?Combinatorics is Algebra and Algebra is Combinatorics.**

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**bronxsystem****Member**- Registered: 2013-06-22
- Posts: 63

hey thanks

any chance you can break down how you solve 7a - 5b = 5 ><

my book doesn't explain it

not being lazy i was able to do the earlier ones but just hit a wall here plzzzzzzzzzz tips and tricks

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**bronxsystem****Member**- Registered: 2013-06-22
- Posts: 63

is this the proper working?

a+b = 23

a = 23 - b

7a - 5b = 5

7 (23 - b) - 5b = 5

151 - 7b - 5b = 5

-7b - 5b = 156

12b = 156

b = 13

and second number easy but does that working make sense?

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**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 6,423

hi bronxsystem

Welcome to the forum.

I'll go through it line by line

a+b = 23

a = 23 - b **OK**

7a - 5b = 5

7 (23 - b) - 5b = 5 **OK**

151 - 7b - 5b = 5 **hhmmmm I make that 161 - 7b -5b = 5**

**So then it should be -12b = - 156 not ** -7b - 5b = 156

**Multiply both sides by -1**

12b = 156 **back on track here but would you have got this without knowing bobbym's answer?**

b = 13 **OK**

**So, some lines correct, but your mistakes sort of cancelled each other out. **

If you want more practice have a look at

http://www.mathsisfun.com/algebra/syste … tions.html

There's a long explanation of the methods you can use (which you could look at or skip if you feel confident, I think) but at the bottom there's a set of questions to try.

Bob

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

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**bronxsystem****Member**- Registered: 2013-06-22
- Posts: 63

oops yeah i see what happened

161 - 7b - 5b = 5

-7 - 5b = -156

-12b = -156

b = 13

thanks for link and help all (:

*Last edited by bronxsystem (2013-06-23 01:47:32)*

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 87,200

Hi bronxsystem;

I am hoping that you can formulate the problem. That is how to translate the words into mathematical statements.

Although I am of the type that is more interested in how then why, the ability to set the problem up is equally important.

**In mathematics, you don't understand things. You just get used to them.Of course that result can be rigorously obtained, but who cares?Combinatorics is Algebra and Algebra is Combinatorics.**

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**bronxsystem****Member**- Registered: 2013-06-22
- Posts: 63

i understand thanks ^^

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 87,200

Hi;

Okay, you are welcome.

**In mathematics, you don't understand things. You just get used to them.Of course that result can be rigorously obtained, but who cares?Combinatorics is Algebra and Algebra is Combinatorics.**

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