—-> Amount = simple interest + principal

—-> 9200 = simple interest + 8000

—-> simple interest = 9200 – 8000
—-> = Rs 1200
—-> if r % be the rate of interest ,
—-> Then from, simple interest = ((principal * rate% * time)/100)
—-> 1200 = ((8000 * r * 3)/100)
—-> r = 5%
—-> 2% more interest that is 7% interest
—-> simple interest = ((8000 * 7 * 3)/100)
—-> = Rs 1680
—-> thus amount he will get is Rs 8000 + Rs 1680 = Rs 9680

A certain sum of money at simple interest amounts to Rs.1260 in 2 years

The same sum of money at simple interest amounts to Rs.1350 in 5 years

Formula used:

S.I = ( P × N × R)/100

Calculation:

Let the Principal be P

S.I for 3 years = 1350 – 1260 = Rs.90

⇒ S.I for 1 year = 90/3 = Rs.30

⇒ S.I for 2 years = 30 × 2 = Rs.60

∴ Principal, P = 1260 – 60 = Rs.1200

Now,

S.I = ( P × N × R)/100

60 = (1200 × 2 × R)/100

∴ R = (60 × 100)/(1200 × 2) = 2.50%

∴ Rate of interest is 2.50%

Explanation: Let the sum invested in Scheme A be x and that in Scheme B be (13900 – x).

Then, (x x 14 x 2)/100 + ((13900 – x) x 11 x 2)/100 = 3508

28x – 22x = 350800 – (13900 x 22)

6x = 45000

x = 7500.

So, sum invested in Scheme B = (13900 – 7500) = 6400.

Let the sum be P.
—> Then, ((P * 7 * 23)/12 * 100) – ((P * 7 * 19)/ 12 * 100 ) = 672
—> or, 161P – 133P = 672 * 100 * 12
—> P = ((672 * 100 * 12)/28) = Rs. 28800

Let the sum be Rs. x. Then, S.I in 20 years = Rs. (3x-x) = Rs.2x
Rate = (100*S.I/ R*T) = (100*2x/x*20) % P.a. = 10% P.a.
Now, sum = Rs. x, Rate = 10% P.a., S.I = Rs. x.
∴ Time = (100*s.I/ P*R) = (100*x/x*10) years = 10 years.