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In a certain class, the ratio of girls to boys is 5:4. How many girls [#permalink]
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22 Sep 2013, 13:57
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In a certain class, the ratio of girls to boys is 5:4. How many girls are there? (1) If four new boys joined the class, the number of boys would increase by 20%. (2) If the number of girls increases by 50%, then after such an increase, the probability that a randomly chosen student would be a boy would be 8/23
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Re: In a certain class, the ratio of girls to boys is 5:4. How many girls [#permalink]
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Dhairya275 wrote: In a certain class, the ratio of girls to boys is 5:4. How many girls are there?
(1) If four new boys joined the class, the number of boys would increase by 20%.
(2) If the number of girls increases by 50%, then after such an increase, the probability that a randomly chosen student would be a boy would be 8/23
Easy one ! but still not able to think any easy way out ! Help Please 1) G/B = 5/4. 4x + 4 = 1.2 * 4x You can find x and hence ans. 2) 8/23 = 4x/(9x +2.5x) x will cancel. So only A stands.
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Re: In a certain class, the ratio of girls to boys is 5:4. How many girls [#permalink]
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22 Sep 2013, 23:37
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Dhairya275 wrote: In a certain class, the ratio of girls to boys is 5:4. How many girls are there?
(1) If four new boys joined the class, the number of boys would increase by 20%.
(2) If the number of girls increases by 50%, then after such an increase, the probability that a randomly chosen student would be a boy would be 8/23
Easy one ! but still not able to think any easy way out ! Help Please In a certain class, the ratio of girls to boys is 5:4. How many girls are there?(1) If four new boys joined the class, the number of boys would increase by 20%. This implies that 4 boys constitute for 20% of the original #of boys. Thus there are 20 boys in the class > there are 25 girls in the class. Sufficient. (2) If the number of girls increases by 50%, then after such an increase, the probability that a randomly chosen student would be a boy would be 8/23: \(\frac{boys}{(girls*1.5+boys)}=\frac{8}{23}\); \(\frac{4x}{(5x*1.5+4x)}=\frac{8}{23}\); \(\frac{4x}{(11.5x)}=\frac{8}{23}\); x cancels: \(\frac{4}{11.5}=\frac{8}{23}\). Not sufficient. Answer: A.
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Re: In a certain class, the ratio of girls to boys is 5:4. How many girls [#permalink]
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01 Nov 2016, 05:08
stmt1. 4x+4 = (1.2) (4x) => 5=x
stmt2. no real numbers are given so it is not sufficient.



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Re: In a certain class, the ratio of girls to boys is 5:4. How many girls [#permalink]
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02 Jul 2017, 14:55
(2) If the number of girls increases by 50%, then after such an increase, the probability that a randomly chosen student would be a boy would be 8/23 > boys/(girls*1.5+boys)=8/23 > 4x/(5x*1.5+4x)=8/23 > 4x/(11.5x)=8/23 > x cancels: 4/11.5=8/23. Not sufficient.
Answer: A.[/quote]
Doesn't 8/23 imply that there are 8 boys out of 23 total people? What am I missing?



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In a certain class, the ratio of girls to boys is 5:4. How many girls [#permalink]
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03 Jul 2017, 02:49



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Re: In a certain class, the ratio of girls to boys is 5:4. How many girls [#permalink]
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09 Apr 2018, 21:34
For Statement (2) 
If you set it up as 1.5(5x) = 15/23, you can get a unique value for x and therefore a value for 5x (which is the ratio of girls). Why is that not sufficient?
Thanks very much in advance



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Re: In a certain class, the ratio of girls to boys is 5:4. How many girls [#permalink]
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09 Apr 2018, 21:41



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Re: In a certain class, the ratio of girls to boys is 5:4. How many girls [#permalink]
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11 Apr 2018, 08:26
Bunuel  thanks for the response. My logic is as follows. Start with the following statement: (2) If the number of girls increases by 50%, then after such an increase, the probability that a randomly chosen student would be a boy would be 8/23 If this is the case, then given that the original proportion of Girls to Boys is 5x : 4x, then girls have increased to 1.5*(5x). After this increase, the total probability that is would be a girl is 1  8/23, or 15/23. As a result, I can set up the following equation below and solve for x, which will solve for the total number of girls? 1.5*(5x) = 15/23



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Re: In a certain class, the ratio of girls to boys is 5:4. How many girls [#permalink]
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11 Apr 2018, 08:32
KNA32 wrote: Bunuel  thanks for the response. My logic is as follows. Start with the following statement: (2) If the number of girls increases by 50%, then after such an increase, the probability that a randomly chosen student would be a boy would be 8/23 If this is the case, then given that the original proportion of Girls to Boys is 5x : 4x, then girls have increased to 1.5*(5x). After this increase, the total probability that is would be a girl is 1  8/23, or 15/23. As a result, I can set up the following equation below and solve for x, which will solve for the total number of girls? 1.5*(5x) = 15/23 You are making the same mistake... 15/23 as well as 8/23 represent probability, which is a ratio. The left hand side should be (girls)/(total) = 1.5*(5x)/(1.5*(5x) + 4x)
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