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1) How many coins, each radius 0.75 cm and thickness 0.2 cm, have to be melted to make a right circular cylinder
of height 8 cm and base diameter 6 cm?
The diameter of each coin is 1.5 cm, and you need = = 16 coins to get an equivalent base area.
Then you need = 40 layers of coins of thickness 0.2 cm to get the height of 8 cm.
Now multiply 16*40 = 640, and you will get the required number of coins.
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2) Water is being pumped into a water tank of dimensions 10 m X 7.5 m X 4 m at the rate of 400 L per minute.
What is the time taken to fill the tank complete?
Volume of the tank 10*7.5*4 = 300 divide by the rate 0.4 : = 750 minutes = hours.