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The ratio of incomes of two persons is 9 : 7 and the ratio of their expenditures is 4 : 3. If each of them manages to save Rs. 2,000 per month, their monthly incomes are

  • A.Rs. 36,000 and Rs. 28,000
  • B.Rs. 27,000 and Rs. 21,000
  • C.Rs. 18,000 and Rs. 14,000
  • D.Rs. 9,000 and Rs. 7,000

Answer: C

The incomes are Rs. 18,000 and Rs. 14,000.

Let the incomes be 9x and 7x and the expenditures 4y and 3y. Each saves Rs. 2,000:

\[ \begin{aligned} 9x - 4y &= 2000 \\ 7x - 3y &= 2000 \end{aligned} \]

Multiply the first by 3 and the second by 4 and subtract:

\[ \begin{aligned} 27x - 28x &= 6000 - 8000 \\ x &= 2000 \end{aligned} \]

So the incomes are 9 × 2000 = 18,000 and 7 × 2000 = 14,000 (expenditures 16,000 and 12,000, ratio 4 : 3). The other pairs have the right 9 : 7 ratio but give different savings.

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