Natalie completely fills a paddling pool with water in 18 minutes. When full, the paddling pool holds a volume of 1404 litres. Work out the average rate at which Natalie filled the paddling pool with water.
A rate means the speed at which something is happening — in this case that’s the
speed at which Natalie is filling the paddling pool with water. We know that the total time taken to fill the paddling pool is 18 minutes and the
total volume of water needed is 1404 litres.
To work out the average rate at which Natalie filled the paddling pool, we need to
divide the total volume of water by the total time taken as this will tell us the
average number of litres of water they were put into the paddling pool in each
minute. This will only be an average rate as we don’t know that Natalie poured the water in
to the paddling pool at a constant rate for the whole of the 18 minutes. 1404 divided by 18 is 78.
Now, if you weren’t sure what calculation you need to use to work out the rate or
perhaps you know you need to do a division but you’re not sure which way around you
should be dividing, there’s actually a clue in the answer box for this question. The units for the answer are litres per minute. That diagonal line means we need to divide a quantity measured in litres by a
quantity measured in minutes.
So we divide the total volume of 1404 litres by the total time of 18 minutes. If we did the division the other way around, the units will be minutes per litre
which doesn’t make sense as the units for a rate.
The average rate at which Natalie filled the paddling pool with water is 78 litres