Maths : Basic Numeracy

Q 170 / 370

UPSC CSE Prelims 2021

A person P asks one of his three friends X as to how much money he had. X replied, “If Y gives me Rs 40, then Y will have half of as much as Z, but if Z gives me @ 40, then three of us will have equal amount.” What is the total amount of money that X, Y and Z have?

EXPLANATION

Correct Option

Let the initial amounts of money with X, Y, and Z be represented by Rs. x, Rs. y, and Rs. z, respectively.

From the first condition, "If Y gives me Rs 40, then Y will have half of as much as Z":

  • X's money becomes x+40
  • Y's money becomes y−40
  • Z's money remains z

The condition translates to the equation: y−40=z2

This simplifies to: 2y−80=z (Equation 1)

From the second condition, "if Z gives me Rs 40, then three of us will have equal amount":

  • X's money becomes x+40
  • Y's money remains y
  • Z's money becomes z−40

This condition implies that the amounts are equal: x+40=y=z−40

From x+40=y, we derive: x=y−40

From y=z−40, we derive: z=y+40 (Equation 2)

Now, substitute Equation 2 into Equation 1:

y+40=2y−80

Rearranging the terms to solve for y:

40+80=2y−y

120=y

Thus, Y has Rs. 120.

Using the value of y, calculate x and z:

  • x=y−40=120−40=80
  • z=y+40=120+40=160

Therefore, X has Rs. 80, Y has Rs. 120, and Z has Rs. 160.

The total amount of money X, Y, and Z have is the sum of their individual amounts:

Total = x+y+z=80+120+160=360

The total amount is Rs. 360.

Incorrect Options

Options 1 (Rs 420), 3 (Rs 300), and 4 (Rs 270) are incorrect. The unique solution derived from the given conditions establishes the total amount as Rs. 360. Any other total would contradict the mathematical relationships specified in the problem statement.