Missing Number Race
Calculation · Year 2–Year 6
Worksheets for this ↓Fill in the missing number against the clock. Every right answer is a step along the track.
Use this on paper
Fact families for addition and subtraction to 20, on paper, for Year 2.
Fact Families - Addition and Subtraction Facts to 20 · £1.50 a sheet, or any 5 for £5 · No subscription.
About the missing number race
A number sentence with one number covered, like □ + 20 = 100, and a set time to fill in as many as you can. Every right answer moves the racer one step along the track, and the next question comes straight up.
The covered number is either of the two on the left, never the answer, so a class has to work backwards. That is what inverse operations means: 100 − 20 finds the missing number in □ + 20 = 100, and the same child needs a different sum for 100 − □ = 60.
Two to six children or teams race, one at a time, each in their own colour, and you choose how many on the board before the first go. When a racer's time is up they stay on the track where they finished, faded, so the next racer can see them coming up and find out whether they get past. The standings along the top keep everyone in order, and when the last racer has gone the board says who won. Solo is one pupil racing their own best go, which suits a one to one session on a tablet.
There is no finish line. How many answers make a good turn depends on the class, the operation and the size of the numbers, so the furthest racer wins.
The clock is a stopwatch with six segments rather than a count of seconds. A segment goes every sixth of the time, and the one running out pulses as the watch ticks, so a class can see roughly how long is left without counting down to the last second. Each racer gets 30 seconds, or 1, 2 or 3 minutes.
How to use it on your whiteboard
- 1Choose the operation on the toolbar: +, −, × or ÷.
- 2Open Numbers to choose how many digits the two numbers have, whether they are round numbers like 20 and 300 or any numbers like 37 and 452, and how long each racer gets: 30 seconds, or 1, 2 or 3 minutes.
- 3Choose the racers: runners, racing cars, bikes or space rockets.
- 4Before the first go, choose how many are racing on the board, from two to six. For one pupil, press Solo instead and they race their own best go.
- 5Press Go. Type the missing number on the keypad and press Submit. A wrong answer shakes and clears so they can try again, and Pass skips a question they are stuck on.
- 6When the time is up, the board shows how many they got right and where that puts them, and the Go button names who is next. New race clears the track.
Questions
- What do the digit buttons mean?
- They are how many digits the two numbers before the equals sign have. 2 and 2 gives questions like 30 + 40, 2 and 3 gives questions like 20 + 100, and 1 and 2 gives divisions like 84 ÷ 7. Every division comes out exactly, and 1 and 1 has only a handful of divisions in it, so for times table facts in reverse use 1 and 2.
- Does it ever go below nought?
- No. A subtraction always takes the smaller number from the bigger one, and a division always divides exactly, so every missing number is a whole number.
- What happens if I change the operation half way through a race?
- The race starts again, because racers on different questions are not in the same race, and the board says so. Press Undo and the whole race comes back. Switching to a different kind of racer does not restart it.
- Does Solo remember a pupil's best score?
- For as long as the page is open. It races their best go as a faded ghost and says when they beat it. Close the page or press Start again and it starts from nothing, because nothing about a pupil is saved anywhere.
- Can I type the answers on a keyboard?
- Yes. The number keys, Backspace and Enter all work, which is handy on a laptop. The keypad on the board is for the child standing at it.
- Do I need an account?
- No. Trove Tools is free with no login, no subscription and no limits.