CAT 2018 Slot 1QA Question 11

RatioEasy

Raju and Lalitha originally had marbles in the ratio 4 : 9. Then Lalitha gave some of her marbles to Raju. As a result, the ratio of the number of marbles with Raju to that with Lalitha became 5 : 6. What fraction of her original number of marbles was given by Lalitha to Raju?

Answer & solution

Correct answer: 7/33

  • A

    6/19

  • B

    1/5

  • 7/33

  • D

    1/4

Solution

Easy

Start Raju and Lalitha at 4x4x and 9x9x marbles. Lalitha gives yy to Raju, making the ratio 5:65:6. Solve for yy in terms of xx, then the required fraction is yy divided by Lalitha's original 9x9x.

1

Set up the new ratio. Raju gains yy, Lalitha loses yy.

4x+y9xy=56\begin{aligned} &\frac{4x + y}{9x - y} = \frac{5}{6} \end{aligned}
2

Solve for yy. Cross-multiply and collect.

6(4x+y)=5(9xy) 24x+6y=45x5y(expand) 11y=21x y=21x11\begin{aligned} &6(4x + y) = 5(9x - y)\\ &\Rightarrow\ 24x + 6y = 45x - 5y \quad\text{(expand)}\\ &\Rightarrow\ 11y = 21x\\ &\Rightarrow\ y = \frac{21x}{11} \end{aligned}
3

Fraction of Lalitha's original marbles. Divide yy by 9x9x.

y9x=21x/119x=2199=733\begin{aligned} &\frac{y}{9x} = \frac{21x/11}{9x} = \frac{21}{99} = \frac{7}{33} \end{aligned}
733    option (c)\boxed{\dfrac{7}{33} \;\Rightarrow\; \text{option (c)}}

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CAT 2018 Slot 1 QA Q11: Raju and Lalitha originally had marbles in the ratio 4 : 9. Then Lalitha gave some of her marbles to Raju. As — Solution | TheCATExam