Question: In January, the value of a stock increased by 50%; and in February, it decreased by 20%. In March, it increased by 25%; and in April, it decreased by 10%. If a person invested Tk. 200 in the stock on January 1 and sold it at the end of April, what was the percentage change in the price of the stock?

Solution:
At the end of January,
The value of the stock is = Tk. 200 + 50% of (Tk. 200)
= Tk. 200 + Tk. 100 = Tk. 300.

At the end of February,
The value of the stock is = Tk. 300 - 20% of (Tk. 300)
= Tk. 300 - Tk. 60 = Tk. 240.

At the end of March,
The value of the stock is = Tk. 240 + 25% of (Tk. 240)
= Tk. 240 + Tk. 60 = Tk. 300.

At the end of April,
The value of the stock is = Tk. 300 - 10% of (Tk. 300)
= Tk. 300 - Tk. 30 = Tk. 270.

Now, the percentage change in price is,
= (Change in price/Original price) × 100%
= (270 - 200)/200 × 100%
= (70/200) × 100%
= 35%

Question: The marked price of a watch was Tk. 1500. A customer bought it for Tk. 1080 after getting two successive discounts. The first discount was 20%. What was the second discount rate?

Solution:
Price after first discount (20%),
= 1500 - (20% of 1500)
= 1500 - (1500 × 0.20)
= 1500 - 300
= Tk. 1200

Amount of second discount
= 1200 − 1080
= Tk. 120

∴ Second discount rate
= (Second discount amount/Price after first discount) × 100
= (120/1200) × 100
= 0.10 × 100
= 10%

∴ The second discount rate is 10%.

প্রশ্ন: শতকরা ৬ টাকা হার সুদে ৬০০ টাকা ৬ বছরে সুদে-আসলে কত হয়?

সমাধান:

দেওয়া আছে,

আসল (P) = ৬০০ টাকা

সুদের হার (r) = ৬%

সময় (n) = ৬ বছর

আমরা জানি,

সরল সুদ, I = (Pnr)/১০০

∴ I = (৬০০ × ৬ × ৬)/১০০

∴ I = ২১৬০০/১০০

∴ I = ২১৬ টাকা

সুদে-আসলে = আসল + সুদ

= ৬০০ + ২১৬

= ৮১৬ টাকা

সুতরাং, সুদে-আসলে ৮১৬ টাকা হবে।