Question

a father give 1%of his income to his two sons as pocket money.the elder son gets 80%of the total amount of money given and he spends 80%of his share. If he saves 20 rupee per month determine father monthly income.

Answer 1

Let father's monthly income be x .

Now 

Amount is given To his Sons
= 1 % of his salary = x × 1/100 = x/100

again, Amount is Received by elder Son = 80% of x/100 = 80/100 × x/100
= 80x/10000 = 8x/1000 = x/125

it is given that he spends 80% of his share

So Amount saved by elder son = 20%
so, amount saved by elder son = 20% of amount gained by elder son

= 20 /100 × x/125

= x/625

a/c to question, amount saved by elder son =20 rs.

or, x/625 = 20

or, x = Rs 12,500

Answer 2

Answer:

Total Income of father = Rs 12,500

Step-by-step explanation:

Suppose

Total Income of father = x

Pocket Money Givne to sons = 1% of total income

Pocket Money Givne to sons = 0.01x

Elder son's Share = 80% of the pocket money

Elder son's Share = 0.8(0.01x)

Elder son's Share = 0.008x

Amount Spent by Elder Son = 80% of share

Amount Spent by Elder Son =0.8(0.008x)

Amount Spent by Elder Son =0.0064x

Amount Saved by Elder Son =  0.008x - 0.0064x

Amount Saved by Elder Son = 0.0016x

As we know

Amount Saved by Elder Son = 20

So,

0.0016x = 20

x = 20÷0.0016

x = Rs. 12,500