A rectangular tank measuring 60cm by 40cm by 20cm was 1/6 filled
with water. At 0800, Tap A with water flowing out at a rate of 3l
per minute was turned on. At 0802, Tap B was turned on to drain
water out of the container at a fixed rate. At 0813, the tank was
75% filled with water. At what time would the tank be filled to the
brim? (1l = 1000cm3).
Volume of tank = 60cm X 40cm X 20 cm = 48000cm^3 = 48L
1/6 of tank = 1/6 X 48L = 8L
Since rate of tap is at 3L per min, after 2 mins,
amount of water in tank = 8L + ( 3L X 2 ) = 14L
75% of tank = 75% X 48L = 36L
Amount of water filled up in 11 mins after drainage is on
= 36L - 14L = 22L
By right, amount of water filled up in 11 mins
= 11 X 3L = 33L
Amount of water lost in 11 mins = 33L - 22L = 11L
Amount of water lost per min = 11L / 11 min = 1L per min
Overall amount of water entering the tank per min = 3L - 1L =
2L
Volume of tank left needed to be filled up = 48L - 36L = 12L
Amount of time more needed to fill up the tank = 12L / 2L = 6
mins
Time when tank will be filled to the brim = 0813 + 6 mins =
0819