Different Types of Rates Questions in PSLE Math Papers
Students usually stumble when they meet this type of rates questions in PSLE Math papers. You need to understand the different types of Rates questions for PSLE Math. Each type will test a different concept.
Firstly, Rates is similar to Speed which means how fast something changes.
Speed is how fast something moves.
Working Rate is how fast a person takes to complete a job.
Water Rate is how fast the water flows in or out from a tank.
Printing Rate is how fast a printer print.
To find the Rate, you need to take the Quantity divide by time taken.
To find speed, you take Distance divide by Time.
If Ahmad takes 5 days to complete painting a house, his rate will be 1 ÷ 5 = 1/5.
If Ahmad takes 5 days to complete painting 2 houses, his rate will be 2 ÷ 5 = 2/5.
Do you get the idea?
After you know what Rates are and how to find them, let’s explore the different types of Rates Questions.
1. Combined Rates
Marcus takes 2 hours to clean a house on his own. Edmund takes 3 hours to clean a house on his own. If they work together, how long will they take to clean a house?
In this example, you can add both their rates together as they work together.
Rate of Marcus –> 1 ÷ 2 = 1/2.
Rate of Edmund –> 1 ÷ 3 = 1/3.
Rate of Marcus Plus Rate of Edmund –> 1/2 + 1/3 = 5/6
Time Taken –> 1 ÷ 5/6 = 1.2 hours
2. Individual Rates
Printer A can print a certain number of pages in 7 hours. Printer B can print the same number of pages in 3 hours. Both printers started printing at the same time for 5 hours. How many pages can Printer B print if Printer A printed 1800 pages in the 5 hours?
In this example, you cannot add their rates together. You need to find their rates individually.
Rate of Printer A –> 1800 ÷ 5 = 360
360 x 7 = 2520
Rate of Printer B –> 2520 ÷ 3 = 840
840 x 5 = 4200 pages
3. Partial Rates
Peter can paint a house in 5 days while John can paint a house in 10 days. Peter started painting alone for 2 days, followed by John joining him to paint the house after that. How long will they take in total to complete painting the house?
Rate of Peter –> 1 ÷ 5 = 1/5
Rate of John –> 1 ÷ 10 = 1/10
In 2 days, Peter can complete –> 1/5 x 2 = 2/5
Remaining part of the house –>1 − 2/5 = 3/5
Rate of Peter plus John –> 1/5 + 1/10 = 3/10
Days needed to paint the remainder –> 3/5 ÷ 3/10 = 2 days
Total Days –> 2 + 2 = 4 days