Total no of students =R

Teacher birthday present costs=y dollars

no of students failed=x

let y=100
R=10
and x=5

then for R students it costs 10 dollars per head

so forR-x students it costs 100/5==>20


so plugin the values to get 20


only B satisfies

thats what i thought but the answer is supposedly D.....CONFUSED...

Y/R is the money each student have to contribute as their first plan

Y/(R-x) is the money each remaining student contribute after x students fail

the additional money each student contribute: Y/R - Y/(R-x) = Yx/R(R-x)

D is the answer.

sibbineni wrote:Total no of students =R

Teacher birthday present costs=y dollars

no of students failed=x

let y=100
R=10
and x=5

then for R students it costs 10 dollars per head

so forR-x students it costs 100/5==>20


so plugin the values to get 20


only B satisfies

If we plug in the above values answer cannot be B, since the question is asking about additional dollars not the whole amount.

It is not a right choice of numbers to plug in because A and D both will give us the same answer.

Try using values R=4, Y=20, X=2. or R=25, Y=100, X=5. This will give only D as an answer.

But I must say the method used by you of plugging in numbers is the best for solving variable questions such as these. But make sure you test all the options before marking the answer!!!!