Never subtract times the way you subtract ordinary numbers. Time runs in sixties, not tens, and column subtraction quietly produces nonsense.
Count up in chunks instead. It is slower to describe and faster to do.
Maths carries 25% of the marks. Almost all of it arrives as worded problems rather than bare calculations, so the reading is part of the maths.
Never subtract times
Ask a child for the gap between 14:35 and 16:10 and many will write it as a subtraction, get 1:75 or 2:25, and move on satisfied.
The reliable method is to count forwards in pieces:
- Jump to the next whole hour.
- Jump in whole hours as far as you can.
- Add the remaining minutes.
- Add the pieces up.
Two worked durations
From 14:35 to 16:10
- 14:35 to 15:00 is 25 minutes
- 15:00 to 16:00 is 1 hour
- 16:00 to 16:10 is 10 minutes
- Total: 1 hour and 35 minutes
A train leaves at 09:48 and arrives at 11:22
- 09:48 to 10:00 is 12 minutes
- 10:00 to 11:00 is 1 hour
- 11:00 to 11:22 is 22 minutes
- Total: 1 hour and 34 minutes
Note how the awkward numbers never had to be subtracted from each other.
Reading a timetable
Timetable questions are comprehension questions with numbers in them. The maths is easy; the reading is where it goes wrong.
- Find the right column first, then the right row. Put a finger on each.
- Check whether times are 12 or 24 hour. 3:40 and 15:40 are not the same question.
- Watch for a dash or a blank, which usually means that service does not stop there. Children read the next row down instead.
- Re-read what is asked. The latest train that arrives before 10am is a different question from the train that takes the least time.
Speed, distance and time
One formula, rearranged three ways:
| To find | Do this | Example |
|---|---|---|
| Speed | Distance divided by time | 120 miles in 2 hours is 60 mph |
| Distance | Speed times time | 60 mph for 3 hours is 180 miles |
| Time | Distance divided by speed | 150 miles at 50 mph is 3 hours |
The trap is units. If a journey takes 90 minutes, that is 1.5 hours, not 1.3. Convert minutes into a decimal of an hour before dividing, or the answer will be wrong in a way that looks right.
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Counting up is slower to explain and faster to do
Time is one of those topics where children who are perfectly good at arithmetic come unstuck, because they apply a method that works everywhere else and fails here. You cannot borrow across a column when the column is worth sixty.
Counting up in chunks takes longer to describe than it does to perform. Twenty five minutes to the hour, an hour, ten minutes. A child can do that in their head in a few seconds once it is a habit, and it never goes wrong.
The timetable questions are really comprehension questions wearing a maths costume, which is the pattern across this whole paper. The arithmetic in them is trivial. Finding the right row and column, and noticing what was actually asked, is the part worth practising.
Mushtaque Ahmed, Founder of GrammarPath and Bright Mentors
Frequently asked questions
How do you work out the time between two times?
Count up in chunks rather than subtracting. From 14:35 to 16:10: 25 minutes to the hour, then 1 hour to 16:00, then 10 minutes, giving 1 hour 35 minutes. Column subtraction produces nonsense because time runs in sixties.
Why do children get time questions wrong?
Usually because they subtract times as if they were ordinary numbers, producing answers like 1:75. Counting forward in pieces avoids the problem entirely and is faster in practice.
How do you read an 11+ timetable question?
Find the column first and then the row, with a finger on each. Check whether times are 12 or 24 hour, and watch for dashes meaning a service does not stop there, since children often read the next row down instead.
What is the speed formula for the 11+?
Speed is distance divided by time, distance is speed times time, and time is distance divided by speed. So 120 miles in 2 hours is 60 miles per hour.
How do you convert minutes for a speed calculation?
Express them as a decimal of an hour before dividing. 90 minutes is 1.5 hours, not 1.3, and getting this wrong produces an answer that looks plausible but is incorrect.