Question

The monthly incomes of two persons are in the ratio of 4 : 5 and their monthly expenditures are in the ratio of 7 : 9. If each saves Rs 50 a month, then sum of their monthly incomes is

Answer 1

Let the monthly income of one person be $4x$ and that of the other be $5x$
Let the monthly expenses of one person be $7y$ and that of other be $9y$

According to the question,

$4x-7y=50........\left(1\right)$

$5x-9y=50........\left(2\right)$

On solving both equations, we get

$y=50$

$x=100$

Therefore,

Monthly income of one person

$=4\times 100=400$
Monthly income of the other person

$=5\times 100=500$

So, the sum of their monthly incomes

$=400+500=900$

Hence, this is the answer.