90 students represent x percent of the boys at Jones Elementary School. If the boys at Jones Elementary make up 40% of the total school population of x students, what is x?
125
150
225
250
500
(B)
The MGMAT explanation doesn't make sense to me. I guess I'm not understanding their method.
Can someone simplify this question for me and do this question both by picking answer choices and algebra?
Thanks =)
X % of boys at Jones elementary
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took sometime to understand the question. I did the pick number way, then saw how the algebra worked, lol.
so pick a mid number, x=225
90 of boys = 225% --> 90/b = 2.25
so b = 90/2.25, b = 40
boys make up 40% of total population X
so b/x = 40% --> 40/225 = 17%, NO
so not C. 17% is too low, to increase it, X has to be smaller. Try B
x = 150
90/b = 150, b = 60
60/150 = 40%, YES
Algebraically (from back solving)
90/boys = x%
boys/x (total population) = 40%
x can be solved
so pick a mid number, x=225
90 of boys = 225% --> 90/b = 2.25
so b = 90/2.25, b = 40
boys make up 40% of total population X
so b/x = 40% --> 40/225 = 17%, NO
so not C. 17% is too low, to increase it, X has to be smaller. Try B
x = 150
90/b = 150, b = 60
60/150 = 40%, YES
Algebraically (from back solving)
90/boys = x%
boys/x (total population) = 40%
x can be solved
the best way to approach such problem is go the way it says....
90=x/100 of boys --------1
boys = 40/100 of x---------2
Put 2 in 1 we get
90=x/100 * 40/100 * x
solve this.. u get 22500=x^2
thus x=150
HTH
90=x/100 of boys --------1
boys = 40/100 of x---------2
Put 2 in 1 we get
90=x/100 * 40/100 * x
solve this.. u get 22500=x^2
thus x=150
HTH
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Let the number of boys = b. We can create the equation:doclkk wrote: ↑Fri Sep 04, 2009 7:41 pm90 students represent x percent of the boys at Jones Elementary School. If the boys at Jones Elementary make up 40% of the total school population of x students, what is x?
125
150
225
250
500
(B)
The MGMAT explanation doesn't make sense to me. I guess I'm not understanding their method.
Can someone simplify this question for me and do this question both by picking answer choices and algebra?
Thanks =)
90 = b * x/100
and
b = 0.4x
Substituting 0.4x for b in the first equation, we have:
90 = 0.4x * x/100
9000 = 0.4x^2
22500 = x^2
150 = x
Answer: B
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