Adding a one-digit number and a two-digit number
To add a one-digit number to a two-digit number, start with the bigger number and count forwards with the smaller number.
43 (larger number) + 8 (smaller number) = 51
You could find the number on a number square and count forwards. Find number 43, then count forwards 8 ones to get 51.
Subtracting a one-digit number from a two-digit number
To subtract a one-digit number from a two-digit number, you also start with the bigger number, but you count backwards.
Try it on the 100 square above.
43 - 8 = 35
Adding two two-digit numbers
When a number problem uses two two-digit numbers, we break down the numbers into tens and ones.
55 + 34 = ?
Start with the tens and add them together.
5 tens + 3 tens = 8 tens
or
50+ 30 = 80
Then add the ones.
5 ones + 4 ones = 9 ones
or
5 + 4 = 9
Finally add both answers together.
80 + 9 = 89
Subtracting two-digit numbers from two-digit numbers
To subtract a two-digit number from a two-digit number we count back the tens of the smaller number and then count back the ones.
What is 58 鈥 44 = ?
44 has 4 tens so we count back 4 tens from the bigger number 58.
58 count back 4 tens:
58, 48, 38, 28, 18
Finally use this answer and then count back the ones:
18 鈥 4 = 14
Therefore:
58 鈥 44 = 14
Top tip!
You can use a one hundred square to help you count backwards and forwards.
Activity 1
Get a piece of paper and a pencil, then listen to this quiz. You only have 10 seconds to answer each question so write the answers down quickly!
Finished? Check your answers . The questions are also written out, if you can't listen to the quiz out loud.
Activity 2
NEW! Play Guardians: Defenders of Mathematica - the winter update. gameNEW! Play Guardians: Defenders of Mathematica - the winter update
It's Mathematica as you鈥檝e never seen it before, with all-new festive backgrounds and costumes. Available for a limited time only. Use your maths skills to save the day before it's too late!
More on Adding and subtracting
Find out more by working through a topic
- count8 of 23
- count10 of 23
- count11 of 23