Question: Every 2 minutes, 5 litres of water are poured into a 1,500 litre tank. After 3 hours, what percent of the tank will be full?

Solution:
In 2 minutes, 5 liters is poured
In 180 minutes = (180 × 5)/2 = 450 liters

So, percentage filled = (450 × 100)/1500
= 30%

Question: A machine is sold at a profit of 20%. Had it been sold for Tk. 60 less, there would have been a loss of 20%. What was the cost price?

Solution:
ধরি, মেশিনটির ক্রয়মূল্য = x টাকা

20% লাভে বিক্রয়মূল্য = x + x এর 20%
= x + 20x/100
= 12x/10

20% ক্ষতিতে বিক্রয়মূল্য = x - x এর 20%
= x - 20x/100
= 8x/10

প্রশ্নমতে,
(12x/10) - (8x/10)= 60
⇒ 4x/10 = 60
⇒ 4x = 60 × 10
⇒ x = (60 × 10)/4
∴ x = 150

∴ মেশিনটির ক্রয়মূল্য = 150 টাকা