SPEED is a P6 Mathematics topic that often confuses students. Here’s a quick look at the five main types of speed questions encountered in the PSLE. Please note that these categories are not meant to be exhaustive and non-routine speed questions may pop out in the PSLE.
1. Foundation Speed Questions
These questions test the foundations that the students have on speed, and requires them simply to compute the answer based on the formula Distance = Speed X Time. E.g. Find the distance Car X travelled from 10 am to 1 pm if its average speed is 75 km/h.
Tip 1: Use the formula
10 – 1 pm = 3 hours 3 hours X 75 km/h = 225 km
2. Opposite Direction – Closing the Gap
These questions test the students on scenarios whereby 2 objects will start from different points and meet each other.
E.g. Town X and Town Y are 600 km apart. A car travels at an average speed of 90 km/h from Town X to Town Y. At the same time, a bus travels at an average speed of 60 km/h from Town Y to Town X. How far would each vehicle have travelled when they meet on their way?
Tip 1: When the car and bus meets, the distance covered by car and bus is equal to the dist between Town X and Y Tip 2: You may make a list of the distance each vehicle travels in an hour and work your way towards the meeting point.
Every hour, car covers 90 km while bus covers 60 km. They will cover 150 km each hour. 600 km divided by 150 = 4 hours They will be travelling for 4 hours before meeting each other, so the car will travel 360 km while the bus will travel 240 km.
3. Opposite Direction – Opening the Gap
These questions test the students on scenarios whereby 2 objects start from the same location and drive away from each other.
E.g. Mr Lee and Mr Tan started driving from Point A in opposite directions. After driving for 4 hours, they were 660 km apart. If Mr Lee’s driving speed was 100 km/h, find Mr Tan’s average driving speed.
Tip 1: As they are moving away from each other, calculate the distance covered by 1 driver first.
If Mr Lee’s driving speed is 100 km/h, he will travel 400 km in 4 hours. Mr Tan would have covered 660 km – 400 km = 260 km Mr Tan’s average speed = 260 km / 4 = 65 km/h
4. Same Direction – Closing the Gap
These questions test the students on scenarios whereby 2 objects start from the same location, but at different speeds and one will catch up with the other.
E.g. At 10.30 a.m., a cyclist started travelling on a road at an average speed of 30 km/h. At 2.30 p.m., a motorist started from the same place, travelling on the same road. If the motorist took 4 h to catch up with the cyclist, find his average speed.
Tip 1: Calculate the total number of hours travelled at the point of the catching up. Tip 2: Compute the speed from the distance that the motorist travelled.
When the motorist catches up, the cyclist had travelled for 8 hours, so distance travelled by cyclist is 8 X 30 km/h = 240 km Motorist speed = 240 km / 4 hours = 60 km/h
5. Same Direction – Opening the Gap
These questions test the students on scenarios whereby 2 objects start from the same location, at different speeds and one will be further away from another.
E.g. Jon started cycling from Point A to Point B at 7 a.m. at an average speed of 12 km/h. Jon started cycling from Point A to Point B 3 hours later. Jon’s speed is twice of David’s. At what time were the two cyclists 48 km apart?
Tip 1: Find the speed of both men Tip 2: Find distance covered by Jon Tip 3: Remember that when David starts cycling, Jon is still cycling
Jon’s speed is 12 km / h, David’s speed is 6 km/h. After three hours, Jon would have travelled 12 km/h X 3 = 36 km/h. Every hour David rides, Jon is 6 km / h faster than him. 48 km – 36 km = 12 km 12 km / 6 km/h = 2 hours David started at 10 am, so 2 hours later, at 12 noon, they will be 48 km apart.
I hope this is useful and helps to ease some of the upcoming PSLE anxiety for some of the parents in this forum. We parents are often more worried than the kids!