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by schelljo » Tue Jun 23, 2015 4:56 pm
Among the 1,600 students at Hamilton High School, 45% take science courses. If 5/12 of the students taking science courses are taking physics, how many students at Hamilton High School are taking physics?


a.300
b.360
c.400
d.600
e.720
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by Brent@GMATPrepNow » Tue Jun 23, 2015 5:26 pm
schelljo wrote:Among the 1,600 students at Hamilton High School, 45% take science courses. If 5/12 of the students taking science courses are taking physics, how many students at Hamilton High School are taking physics?

a.300
b.360
c.400
d.600
e.720
Among the 1,600 students at Hamilton High School, 45% take science courses.
45% of 1600 = (0.45)(1600)
= (9/20)(1600)
= 720
So, 720 students are taking science courses

If 5/12 of the students taking science courses are taking physics
So, number of physics students = 5/12 of 720
= (5/12)(720)
= [spoiler]300 = A[/spoiler]

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by [email protected] » Tue Jun 23, 2015 5:32 pm
Hi schelljo,

This question is ultimately just about multiplication, but you can approach the math steps in a couple of different ways (depending on the 'format' that you want to put the numbers in):

Total Students: 1600

45% of those students take science courses....you can write this in a few different ways...

(.45)(1600) =
(45/100)(1600) =

or you can use the '10% trick'....

10% of 1600 = 160
45% = (4.5)(160)

However you want to do the math, you'll end up with....

720 students take science courses.

Next, we're told that 5/12 of THOSE students are taking physics....again, you can choose how you want to organize this information....

(5/12)(720) = 300 taking physics

You could also get to this answer with some estimation. Since 5/12 is LESS than 1/2, we're looking for an answer that is LESS than HALF of 720. There's only one answer that fits...

Final Answer: A

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by GMATGuruNY » Tue Jun 23, 2015 5:44 pm
schelljo wrote:Among the 1,600 students at Hamilton High School, 45% take science courses. If 5/12 of the students taking science courses are taking physics, how many students at Hamilton High School are taking physics?


a.300
b.360
c.400
d.600
e.720
Percentage who take science = 45% = 45/100 = 9/20.

Since the number of physics students is equal to 5/12 of the 9/20 who take science, we get:
(5/12)(9/20)(1600)

= (1/4)(3/4)(1600)

= (3/16)(1600)

= 300.

The correct answer is A.
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by Matt@VeritasPrep » Tue Jun 23, 2015 5:46 pm
You could opt for an algebraic approach as well:

Students taking science = x
Students taking physics = y

We know that x = .45*1600 = 720. We also (sort of) know that (5/12) * x = y, so (5/12) * 720 = y and y = 300.

The problem here is that there might be students taking ONLY physics, so the prompt seems sloppy.
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by schelljo » Tue Jun 23, 2015 7:17 pm
Thanks everyone for their responses. Can you tell me where my approach is wrong. So I made a table as below:

Science Not Science
Physics 300 unknown unknown (FIND)
Not Physics 420 unknown unknown
720 880 Total=1600

45% of 1600 = 720
5/12 of 720 = 300

I guess I read this as where Science and Physics were two different classes, not a category and subcategory. Did I totally misread this or is the wording in the question a bit off here?
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by Matt@VeritasPrep » Tue Jun 23, 2015 7:20 pm
schelljo wrote:Thanks everyone for their responses. Can you tell me where my approach is wrong. So I made a table as below:

Science Not Science
Physics 300 unknown unknown (FIND)
Not Physics 420 unknown unknown
720 880 Total=1600

45% of 1600 = 720
5/12 of 720 = 300

I guess I read this as where Science and Physics were two different classes, not a category and subcategory. Did I totally misread this or is the wording in the question a bit off here?
Your table is a little tough for me to follow, but you've got the right idea.

In theory, we have four groups:

Science only = w
Physics only = x
Both = y
Neither = z

That should give us

w + x + y + z = 1600
(w + y) = .45*1600 = 720
(5/12) * (w + y) = y, or (5/12) * 720 = 300

That tells us y = 300, so 300 students take BOTH classes ... but we still don't know x.
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by Brent@GMATPrepNow » Wed Jan 10, 2018 12:03 pm
schelljo wrote:Among the 1,600 students at Hamilton High School, 45% take science courses. If 5/12 of the students taking science courses are taking physics, how many students at Hamilton High School are taking physics?


a.300
b.360
c.400
d.600
e.720
Among the 1,600 students at Hamilton High School, 45% take science courses.
45% of 1600 = (0.45)(1600)
= (9/20)(1600)
= 720
So, 720 students are taking science courses

If 5/12 of the students taking science courses are taking physics
So, number of physics students = 5/12 of 720
= (5/12)(720)
= 300
= A

Cheers,
Brent
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