My Math Forum

My Math Forum (http://mymathforum.com/math-forums.php)
-   Algebra (http://mymathforum.com/algebra/)
-   -   Ratios (http://mymathforum.com/algebra/16831-ratios.html)

MathematicallyObtuse January 9th, 2011 06:54 AM

Ratios
 
How do I solve this?

In an election for senior class president, Alice received 30 votes more than David. If the ratio of the number of votes Alice received to the number of votes David received was 8 to 7, how many votes did David receive?

I have two unknowns: # of votes David receives = 7/15 times some number to give 30 + some number.

Chimoo January 9th, 2011 07:27 AM

Re: Ratios
 
If the ratio is 8:7 doesn't it just mean that David received 7*30 votes, which is 210? Or am I missing something silly

Or using simultaneous equations:

a - 30 = d
7/8a = d

8a - 240 = 8d
7a = 8d

a - 240 = 0
a = 240
d = 210

soroban January 9th, 2011 07:45 AM

Re: Ratios
 
Hello, Chimoo!

Quote:

If the ratio is 8:7, doesn't it just mean that David received 7x30 votes, which is 210 ?
Or am I missing something silly? [color=beige] . [/color] [color=blue] no![/color]


Absolutely correct!

A terrific "eyeball" solution!


MathematicallyObtuse January 9th, 2011 08:07 AM

Re: Ratios
 
Quote:

Originally Posted by Chimoo
If the ratio is 8:7 doesn't it just mean that David received 7*30 votes, which is 210? Or am I missing something silly

Or using simultaneous equations:

a - 30 = d
7/8a = d

8a - 240 = 8d
7a = 8d

a - 240 = 0
a = 240
d = 210

Delightful! I wouldn't have seen that in a million years! Thank you :-)


All times are GMT -8. The time now is 07:46 AM.

Copyright © 2019 My Math Forum. All rights reserved.