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Re: In a school there are two sections A and B. When a few students from [#permalink]
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Solution


Given:
    • In a school there are two sections A and B.
    • When a few students from section B took transfer to section A the strength of section A increased by 22.5% and strength of B decreased by 30%

To find:
    • Now, what percentage of students in section A should be given a transfer to section B such that section A and section B have the same strengths

Approach and Working Out:
    • Let the strength of sections A and B be A and B respectively
    • If x students take transfer, then the new strengths will be A + x and B - x

Now, we are given that
    • A + x = 1.225A, and
    • B – x = 0.7B
    • Solving two equations, we get, \(A = \frac{4B}{3}\)
      o Implies, \(1.225A = \frac{49A}{40} = \frac{49B}{30}\), and
      o \(0.7B = \frac{7B}{10}\)

Again, if y students are transferred from the new strengths A to B then sections A and B will have equal strength
    • \(\frac{49B}{30} – y = \frac{7B}{10} + y\)
    o Implies, \(y = \frac{7B}{15}\)

Thus, percentage of students to be transferred = \(\frac{7B}{15}/\frac{49B}{30} = \frac{200}{7}%\)

Hence, the correct answer is Option C.

Answer: C
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Re: In a school there are two sections A and B. When a few students from [#permalink]
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It took some time for me to understand this. But here goes..

same no of students have been removed from B and added to A, yet different percentage, so find the relationship.

30% of B = 22.5% of A
which gives, A = (4/3)B

With this, now i can easily frame a number.. Say
A
400 -> 22.5% increase -> 490
B
300 -> 30% dec -> 210

Difference has to be divided by 2 ( since we want them to be the same ) so, 280/2 = 140.

140/490 = 0.28 hence a 28%
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Re: In a school there are two sections A and B. When a few students from [#permalink]
Bunuel wrote:
In a school there are two sections A and B. When a few students from section B took transfer to section A the strength of section A increased by 22.5% and strength of B decreased by 30%. Now, what percentage of students in section A should be given a transfer to section B such that section A and section B have the same strengths?


A. \(\frac{100}{7}\)%

B. 20%

C. \(\frac{200}{7}\)%

D. 40%

E. \(\frac{300}{7}\)%




Let A and B be the initial number of students.
After the transfer of x: A+x = 1.225 A = 49/40 A. Similarly, we have new B = 7/10 B.
Now x = 0.225 A = 0.3 B. So 225A=300B or 3A=4B. A= 3/4B. So new B = 7/10*3/4*A = 21/40 A.

Given y students are transferred another time:

49/40A - y = 21/40A + y
2y = (49-21)/40 A = 28/40A
y = 14/40A = 7/20 A.

So the ratio of student regarding new A is (7/20A)/(49/40A) = (7*40)/(20*49) = (1*2)/(7*1) = 2/7 or (200/7)% of new A.

IMO C.
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In a school there are two sections A and B. When a few students from [#permalink]
Bunuel wrote:
In a school there are two sections A and B. When a few students from section B took transfer to section A the strength of section A increased by 22.5% and strength of B decreased by 30%. Now, what percentage of students in section A should be given a transfer to section B such that section A and section B have the same strengths?


A. \(\frac{100}{7}\)%

B. 20%

C. \(\frac{200}{7}\)%

D. 40%

E. \(\frac{300}{7}\)%



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Poorly worded question.

The word "strength" lacks a clear definition.

Could just as easily and reasonably be interpreted as being percentage of total rather than absolute number, which interpretation would only be discarded after working through most of the calculation.

If "number" is the intended meaning of "strength", just say so, it ain't hard.

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In a school there are two sections A and B. When a few students from [#permalink]
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