Question: Find the rate of discount being given on a shirt whose selling price is Tk. 420 after deducting a discount of Tk. 80 on its marked price.

Solution:
দেওয়া আছে,
বিক্রয়মূল্য = 420 টাকা
কমিশন = 80 টাকা

∴ গায়ে লিখা দাম = (420 + 80) টাকা 
= 500 টাকা

500 টাকায় কমিশন দেয় 80 টাকা
∴ 1 টাকায় কমিশন দেয় 80/500 টাকা
∴ 100 টাকায় কমিশন দেয় (80 × 100)/500 টাকা
= 16 টাকা

Solution:
Interest from Tk. 2000 in 3 years at 5%:
SI = (P × R × T)/100
= (2000 × 5 × 3)/100
= 300 Tk.

Now,
Tk. 1500 to Produce the Same Interest (Tk. 300) at 4%:
Principal, P = Tk. 1500
Interest, SI = Tk. 300
Interest Rate, R = 4%
​ Time, T = ? years

SI = PRT/100
⇒ T = (SI × 100)/(P × R)
⇒ T = (300 × 100)/(1500 × 4)
⇒ T = 30000/6000
∴ T = 5 years

Question: Find the simple interest on BDT 12000 at 8% per annum for 6 months.

Solution:
Principal, P = 12000 Taka
Time, n = 6 months = 6/12 = 1/2 years
Rate of interest, r = 8% = 8/100

Simple Interest, I = P × n × r
= 12000 × (1/2) × (8/100)
= (12000 × 1 × 8)/(2 × 100)
= 96000/200
= 480

∴ The simple interest is Tk. 480.