Primary 2 · Mathematics
P2 time
Written as minutes, 2 h 5 min is 125, not 205. The 205 comes from a year spent counting in tens and hundreds, and time is the one measure that works in sixties.
- Level
- P2
- Usually taught
- Term 2
- Covers
- 1 concept
What changes at P2
Primary 2 reads the clock to the minute, measures time in hours and minutes, and converts between the two: 2 h 5 min as minutes, or 125 min back into hours and minutes. It also uses a.m. and p.m. from the story.
The conversion is where marks go. Everything else your child has converted this year (tens, hundreds, cents) goes up in 10s and 100s. An hour is 60 minutes.
The sentence that costs the mark
A journey took 2 h 5 min. How many minutes is that?
What the working usually does
2 h 5 min =2 h as 200=205 min
Writes the hours as hundreds, as if an hour were 100 minutes.
What the question asked
2 h 5 min =2 h as 120=125 min
Counts each hour as 60 minutes, then adds the 5.
205 looks like a tidy place-value answer, and the 5 is added correctly. Only knowing that an hour is 60 minutes shows the 2 was turned into the wrong number.
| Point | Value (min) |
|---|---|
| 0 | 0 |
| Tick 2 | 20 |
| Tick 3 | 40 |
| 60 | 60 |
| Tick 5 | 80 |
| Tick 6 | 100 |
| 120 | 120 |
| Tick 8 | 140 |
| Tick 9 | 160 |
| Tick 10 | 180 |
| 200 | 200 |
The same question, worked properly
One hour is 60 minutes
1 h = 60 minHave your child say it before touching the numbers. The slip happens when this line is skipped and the 100 fills the gap.
Change the hours
2 h = 60 + 60 = 120 minThis is the step that fails. Count in 60s: 60, 120. Two hours is 120 minutes, not 200.
Add the minutes
120 + 5 = 125 minThe journey took 125 minutes. Going back the other way, take out 60s: 125 is 60 + 60 + 5, which is 2 h 5 min.
How can you tell it has clicked?
Ask how many minutes are in 1 hour, then in 2 hours. If the second answer is 200, the hundreds habit is still in charge.
Then give it the other way: 75 minutes as hours and minutes. "1 h 15 min" means the 60 is understood. "75 is less than 100, so no hours" means it is not.
One thing to try tonight
Set a kitchen timer for 60 minutes and ask your child to guess how many minutes are in 2 hours. Count in 60s together, 60 and then 120, and compare with the guess.
Use a real journey too. If the drive to a grandparent's home takes 1 h 20 min, ask how many minutes that is before you leave.
What your child will meet in this topic
- Time in Minutes
Most Singapore schools introduce this in Term 2, though schools do differ by a term either way. If your child’s school runs a different order, you can set it in the schedule on your dashboard.
What it leads to
P3 works out how long something takes from a start and an end time, and uses the 24-hour clock. Both lean on the same 60.
A child who counts in 60s here will not work out 3.50 p.m. to 4.20 p.m. like an ordinary subtraction in P3, which is where the base-100 habit costs the most marks.
The same topic in other years
It comes back each year and gets harder, so it helps to see what came before and what is coming.
More in Primary 2
Other topics in the same year, so you can see what sits either side of this one.
See how your child is doing on this topic
StudyLah marks each step separately, so you can see whether it was the setup or the arithmetic that cost the mark.