Question

Water is flowing into a tank at a rate of 20 cm3/min. At the start, there is 250 cm3 of water in the tank.

(i) How much water will be in the tank after 30 minutes?
(ii) Find the time when there is 1210 cm3 of water in the tank.

Answer 1

i) 410 cm³

ii) 48 min

Explanation:

we start with 250 cm³.

and then we fill in 20 cm³ per minute.

i)

after 30 minutes we have

250 + 8×20 = 250 + 160 = 410 cm³

ii)

how long (how many minutes) does it take to reach 1210 cm³ in the tank ?

well, first we subtract the start amount (250).

and then we see how often 20 cm³ will "fit" into the remainder. and then we know how many minutes the water has to run.

1210 - 250 = 960 cm³

so, the incoming water needs to reach 960 cm³ to have a total of 1210 cm³.

and

960 cm³ / (20 cm³ / min) = 960 cm³ min / 20 cm³ =

= 960 min / 20 = 48 min