Question

the ratio of incomes of two persons is9:7 and the ratio of expenditure is 4:3.ifeach of them manages to save Rs.2000 per month ,find their monthly incomes

Answer 1

let the gross income multiplier = x
let the expenditure multiplier = y
:
9x - 4y = 200
7x - 3y = 200
:
Multiply the 1st equation by -3, multiply the 2nd equation by 4, results
-27x + 12y = -600
28x - 12y = 800
-------------------addition eliminates y, find x:
x = 200
then
9*200 = $1800 is one income
7*200 = $1400 is the other income
;
:
Check solution by finding the expenditure multiplier
1800 - 4y = 200
-4y = 200 - 1800
-4y = -1600
y = 
y = 400 is the multiplier
then
4(400) = 1600 spent by one guy
3(400) = 1200 spent by the other guy ($200 saved by both)