In a certain physic class, the ratio of the number of physics majors t

Question

In a certain physic class, the ratio of the number of physics majors to non-physics majors is 3 to 5. If two of the physics majors were to change their major to biology, the ratio would be 1 to 2. How many physics majors are in the class?

(A) 16
(B) 18
(C) 24
(D) 30
(E) 32

(A) 16
(B) 18
(C) 24
(D) 30
(E) 32

TestPrepUnlimited · Answer

Set the number of physics majors as  x . Then there are  \frac{5}{3}x  non-physics majors. The new ratio give us:
 \frac{x-2}{\frac{5}{3}x} = \frac{1}{2}

x - 2 = \frac{5}{6}x

\frac{1}{6}x = 2

x = 12  would be the number of physics majors.

Hoozan  maybe something is up with your question?

Hoozan · Answer

Number of Physics majors = 3x
Number of Non-physics majors = 5x (where x is a common ratio multiplier)

Now, if 2 physics majors were to shift to major in biology (Non-physics major) our current number of physics major would reduce by 2 while non-physics would increase by 2

\frac{3x - 2}{5x + 2}  =  \frac{1}{2}

upon solving we get x = 6

So current physics major = 3x = 18 (B)

You mentioned that there are  \frac{5}{3}x  non-physics majors. So when 2 shift to biology shouldn't this ratio change to  \frac{5}{3}  + 2

RohitSinha · Answer

18 is the number of major before 2 getting changed their major to biology
Answer would be 18-2=16

Posted from my mobile device

Hoozan · Answer

RohitSinha  the question uses the word "IF". So that's a hypothetical situation in which 2 were removed. In reality we still have 3x i.e. 18 students as physics majors.

HinalAmin24 · Answer

total = x (Physic and non physic)

P : NP = 3 : 5

So total P = 3/8 * x

now 2 p are shifted then ratio would be P : NP = 1 : 2

3/8*x - 2 = 1/3 *x

x = 48

question is asking for total major Physic = 3/8 * x = 18

ravigupta2912 · Answer

The question is confusing. I voted 16 since I thought the question is asking how many physics majors would be after the shift. If we're to consider prior to shift, then its 18.

I've been through this confusion (whether the Q is asking the number pre change or post change) more than once now and i'm actually worried if this is a thing on GMAT? And if it is, do we just assume that the question is asking for original ratio / number?

Any thoughts?

Hoozan · Answer

The real question is:  The ratio of the number of physics majors to non-physics majors is 3 to 5. How many physics majors are in the class

But you will notice that we don't have enough information to answer the above question. Now when we look at the IF statement "if two of the physics majors were to change their major to biology, the ratio would be 1 to 2." we now are able to solve the main question.

Takeaway:  See the IF statement as additional information to solve the question and not as the question itself

In a certain physic class, the ratio of the number of physics majors t

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In a certain physic class, the ratio of the number of physics majors t

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