principle = (interest x 100) / (time x rate)
= Rs. (100 x 80)/(4 x 2) = Rs. 1000

∴ C.I. =Rs.[{1000 x (1 + 4/100)² - 1000}]

Correct Option: A

principle = (interest x 100) / (time x rate)
= Rs. (100 x 80)/(4 x 2) = Rs. 1000

∴ C.I. =Rs.[{1000 x (1 + 4/100)² - 1000}]
= Rs. 81.60

∵ P x (1 + 20/100)^t > 2P
⇒ (6/5)ⁿ > 2

Correct Option: B

∵ P x (1 + 20/100)^t > 2P
⇒ (6/5)ⁿ > 2
Now, (6/5) x (6/5) x (6/5) x (6/5) > 2
⇒ 1296/615 > 2
∴ t = 4 years

Let P be the principle and R% per annum be the rate. Then,
P(1 + R/100)³ = 10648 ....(i)
and P(1 + R/100)² = 9680 .....(ii)

Correct Option: B

Let P be the principle and R% per annum be the rate. Then,
P(1 + R/100)³ = 10648 ....(i)
and P(1 + R/100)² = 9680 .....(ii)
on dividing (i) by (ii), we have
⇒ (1 + R/100) = 10648/9680
⇒ R/100 =968/9680 = 1/10
∴ R =100/10 = 10%

S.I. on Rs. 500 for 1 year = 540 - 500 = Rs. 40
∴ Rate = (100 x 40)/(500 x 1) = 8%
and Sum = Rs.(100 x 500)/(8 x 1) = Rs. 6250

Correct Option: D

S.I. on Rs. 500 for 1 year = 540 - 500 = Rs. 40
∴ Rate = (100 x 40)/(500 x 1) = 8%
and Sum = Rs.(100 x 500)/(8 x 1) = Rs. 6250

[5000 x (1 +R/100)² - 5000] - (5000 x 2 x R)/100 =72

Correct Option: B

∵ [5000 x (1 +R/100)² - 5000] - (5000 x 2 x R)/100 =72
⇒ 5000[(1 +R/100)² - 1 - R/50] = 72
∴ 1 + R²/10000 + 2R/100 - 1 - R/5 = 72/5000
⇒ R² = (72/5000 x 10000) = 144
∴ R = 12%