A printing machine prints 120 posters in 4 minutes. The machine works at the same rate the whole time. How many posters does it print in 10 minutes?
The machine prints 300 posters in 10 minutes.
Ans: 300
Example 1 of 2
The printing machine prints 30 posters each minute. It must print 450 posters. How many minutes does that take?
It takes 15 minutes.
Ans: 15
Example 2 of 2
A car park charges $3 for the first hour and $2 for every further half hour or part of a half hour. How much does it cost to park there for 2 hours 15 minutes?
Total cost = $6 + $3 = $9
Ans: $9
How to solve it
Draw one bar for the 4 minutes, cut into 4 equal units. Those 4 minutes make 120 posters.
Find the rate first: 120 shared over 4 minutes is 30 posters per minute.
Use the rate for the total: 10 minutes at 30 posters is 10 times 30, which is 300 posters.
To find a time, divide the total by the rate: 450 posters at 30 a minute is 450 divided by 30, which is 15 minutes.
When the rate changes partway, cut the bar at the change: the first hour is 3 dollars on its own.
The other 75 minutes is 2 half hours and a part, charged as 3, at 2 dollars each: 6 plus 3 is 9 dollars.
First find the rate, then solve the problem. And when the rate changes partway, cut the bar at the change and price each stretch. A part of a block is charged as a whole one.
Practice questions with worked solutions
Question 1 is free to try. The other 11 open in the free trial, each with its full working.
How do you solve P5 rate word problems for the total or number of units?
This page teaches the Primary 5 outcome on finding rate, total amount or number of units when the other two are given.
What your child learns here
This page teaches the Primary 5 outcome on finding rate, total amount or number of units when the other two are given. The key move is getting the amount for one unit before anything else.
Rate = total amount ÷ number of units.
Total amount = rate × number of units.
Number of units = total amount ÷ rate.
If the amount given is for several units, share it down to one unit first.
When the rate changes partway, as in charges by bands, each band is worked out on its own.
Does the answer make sense?
At a steady rate, more units must give a larger total, so your child should find that 10 minutes of printing makes more posters than 4 minutes. When two machines or workers run at the same time on one job, they must finish it faster than either one could alone.
How to practise these questions
Basic questions train using a rate to find either a total or a number of units. Intermediate questions add charges that change in steps, rates scaled down and answers in a smaller unit. Challenge questions combine two rates, change a rate partway or compare rates over different counts, so the rate must be settled before anything else. If a rate question stalls, watch the solution film for that question, then try it once more later from Revision.
Questions parents ask
What are the three rate formulas? Rate = total ÷ number of units, total = rate × number of units, and number of units = total ÷ rate. Knowing any two gives the third.
Is rate in the Primary 5 syllabus? Yes. The Primary 5 Rate strand covers rate as an amount per unit, and finding rate, total amount or number of units given the other two.
Does my child need to draw a model for rate questions? It helps when the given amount is for several units. A bar cut into equal units shows the amount for one, and the lesson on this page draws it.
