AchyuthReddy wrote:

Each student in a class to choose an optional subject.If \(\frac{1}{5}\) chose math,\(\frac{1}{4}\)chose biology,\(\frac{1}{2}\) chose history and the remaining 10 chose psychology.what is the number of students in the class?

A) 80

B) 110

C) 160

D) 200

E) 400

Let X be the total no.

so \(x-\frac{x}{5}-\frac{x}{4}-\frac{x}{2} = 10\)

or \(x(1-\frac{1}{5}-\frac{1}{4}-\frac{1}{2}) = 10\)

or \(x = 10 * 20 = 200\)

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Another way to solve ,

just use the number from the solution

it is always advisable to start with option C

So if the total no. = 160,

then \((\frac{1}{5} * 160) + (\frac{1}{4} * 160) + (\frac{1}{2} * 160)\) = not equal to 160

move to option D

if the total no is 200 then

then \((\frac{1}{5}* 200) + (\frac{1}{4} * 200) + (\frac{1}{2} * 200) = 200\)and hence our answer

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