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Read the posting on Sarin learns rate of change in school (Math Concept) to learn about concept of rate of change.
You can read the posting on Sarin learns Perimeter, Area and Volume in school(Math Concept) to learn the concept of volume.
Upper primary school mathematics question UPQ224
Sarin had a rectangular tank with size of 40 cm by 30 cm by 40 cm and it was 1/6 filled with water. At 0930 h, Sarin turned on the Tap X with water flowing out at a rate of 3 l per minute. At 0932 h, Sarin turned on the Tap Y to drained water out of the tank at a fixed rate. At 0943 h, the tank was 75% filled with water. At what time would the tank be filled to the brim?
Solution:
The capacity of the tank = 40 × 30 × 40 = 48 000 cm3
The volume of water in the tank at first = 1/6 × 48 000 = 8 000 cm3
From 0930h to 0943h,
The time duration = 13 min
The water flow rate of tap X = 3 l/min = 3000 cm3/min
Water flow into the tank = 3 000 × 13 = 39 000 cm3
The percentage of water in the tank at 0943h is 75%
The volume of water in the tank at 0943h = 48000 × 75% = 36000 cm3
The volume of water flow out = 8000 + 39000 – 36000 = 11 000 cm3
The rate of water outflow from tank = 11 000 ÷ 11 = 1000 ml/min = 1 l/min
The relative flow rate after 0932h = 3 – 1 = 2 l/min
Another 25% capacity of the tank to fill up from 0943 h
The additional volume of water needed = 48 × 25% = 12 l
Require 12 ÷ 2 = 6 min more to fill up the tank to the brim
At 0949 h, the tank filled to the brim
Solving Primary School Mathematics 