A sum of TK. 800 amounts to TK. 920 in 3 years at simple interest. What will it amount to if the rate of interest is increased by 3%?

Question: A sum of TK. 800 amounts to TK. 920 in 3 years at simple interest. What will it amount to if the rate of interest is increased by 3%?

Solution:
Principal (P) = 800 TK.
Amount after 3 years = 920 TK.
∴ Simple Interest (SI) for 3 years = 920 - 800 = 120 TK.

Now, SI = (P × n × r)/100
⇒ 120 = (800 × 3 × r)/100
⇒ 120 = 24r
⇒ r = 120/24
∴ r = 5%

New Interest Rate = 5% + 3% = 8%
New simple interest for 3 years = (800 × 3 × 8) / 100 = 192 TK.
New Amount = Principal + New Interest = 800 + 192 = 992 TK.

Alternative Shortcut Method:
Additional Interest for 3% increase in 3 years = (800 × 3 × 3)/100 = 72 TK.
∴ New Amount = 920 + 72 = 992 TK.