Answer:

Rate of interest = (√D/√P) × 100 [for 2 years]

Where D = difference in the compound interest and simple interest

P = principal

Calculation:

Rate of interest = (√128/√5000) × 100

⇒ (8/50) × 100 = 16%

∴ Required rate of interest is 16%

I hope it will help you

Verified answer

The amount invested in bank A = 2000, and

the amount invested in bank B = 3000.

Given:

i) A man invested 5,000 partly in bank A and partly in bank B.

ii) The rates of simple interest per annum in two banks are respectively 5% and 6%.

iii) Total interest obtained by him in one year is 280.

To find:

The amount invested in each bank.

Solution:

Let the amount invested in bank A = x.

Therefore,

the amount invested in bank B = 5000 - x

The rate of simple interest per annum in bank A = 5%

=> at the end of one year, the amount of interest man can expect on an investment of x from bank A = (5/100) x

The rate of simple interest per annum in bank B = 6%

=> at the end of one year, the amount of interest man can expect on an investment of (5000 - x) from bank B = (6/100) (5000 - x)

Total interest obtained at the end of one year

                                                              = (5/100) x + (6/100) (5000 - x) = 280

=> (5/100) x + (6/100) (5000 - x) = 280

=> (5/100) x + (6/100) (5000) - (6/100) x = 280

=> (5/100 - 6/100) x + 300 = 280

=> ((5 - 6)/100) x = 280 - 300

=> (-1/100) x = -20

=> x = 2000

Since x = 2000,

Man invested 2000 in bank A and (5000 - 2000) = 3000 in bank B.

Hence,

the amount invested in bank A = 2000, and

the amount invested in bank B = 3000.

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