Ratio PS

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Ratio PS

by angxif » Sun May 16, 2010 5:12 am
The ratio of the number of boys to the number of girls in a certain school club is 3 : 4. If there are 5 more girls than boys in the club, how many girls are in the club?
A. 7
B. 8
C. 12
D. 15
E. 20

Could someone give me an easy explanation to this?
Source: — Problem Solving |

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by gmatjedi » Sun May 16, 2010 7:45 am
boys/girls=3/4=x/(x+5)
x=15
girls=20

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by rajeshsources » Mon May 17, 2010 11:30 pm

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by pradeepkaushal9518 » Tue May 18, 2010 12:22 am
this u can solve by plug in method

choose the answer option

12 if 12 are girls than boys will be 9 as boys:girls = 3:4 but difference is not 5 hence not possible
15 then no of boys cant be solved so not possible
20 then boys will be 15 and the difference is 5 so correct

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by frank1 » Tue May 18, 2010 4:00 am
oh i call it backward solving....seems like it is called plugin method as well
when you start backward solving
it is good to start from option C(not a rule but....)
here the answer was at E so 3 tests only