Option 3 : 3(7 / 11)%

**Given:**

Expenditure on household items = 30%

Share of wife = 20%

Investment = 30% of the remaining amount

The rest amount saved.

**Formulae used:**

Total income = Total expenditure + Total Investment + Total savings

**Calculation:**

Let the total amount be Rs. 1000.

Expenditure on household items = 30% of Rs. 1000 = Rs. 300

Share of wife = 20% of Rs. 1000 = Rs. 200

Remaining amount = Rs. 1000 - (Rs. 300 + Rs. 200) = Rs. 500

Investment = 30% of the remaining = 30% of Rs. 500 = Rs. 150

Savings = Rs. 500 - Rs. 150 = Rs. 350

Interest earned on investment (@20% p.a.) = Rs. 150 × 20% = Rs. 150 × (20 / 100) = Rs. 30

Interest earned on savings (@20% p.a.) = Rs. 350 × 20% = Rs. 350 × (20 / 100) = Rs. 70

Difference in interest = Rs. 70 - Rs. 30 = Rs. 40

Overall income = Rs. 1000 + Rs. 30 + Rs. 70 = 1100

Difference in interest / overall income = 40 / 1100 = 4 / 110

Difference will be [(4 / 110) × 100]% = (40 / 11)%

Difference = 3(7 / 11)% of overall income

**Short tricks:**

As the rate of interest is same for both the cases.

The difference in interest = (Difference between savings and investment) × 20%

= (200) × 20% = 40