Adding and subtracting 2-digit numbers

For grown-ups: this lesson in words

Year 2 · Maths

Adding and subtracting 2-digit numbers: I can add and take away 2-digit numbers.

1. Start on 34. Add 30, which is 3 tens.

   Jump down a row for each ten: 44, 54, 64.

   34 + 30 = 64

   Picture: A hundred square: the numbers 1 to 100 in 10 rows of 10. A marker starts on 34 and jumps down the column ten at a time, landing on 44, 54 and 64. The number 64 is circled.

2. Start on 78. Take away 40, which is 4 tens.

   Up a row for each ten: 68, 58, 48, 38.

   78 − 40 = 38

   Picture: A hundred square: the numbers 1 to 100 in 10 rows of 10. A marker starts on 78 and jumps up the column ten at a time, landing on 68, 58, 48 and 38. The number 38 is circled.

3. Your turn: Start on 25. Add 20. Where do you land?

   Picture: A hundred square: the numbers 1 to 100 in 10 rows of 10. The column from 5 to 95 is outlined. The number 25 is circled.

   Choose one:

   • 27
   • 35
   • 45

   Answer

   The answer: 45

   35, then 45. 25 + 20 = 45

   Picture: A hundred square: the numbers 1 to 100 in 10 rows of 10. A marker starts on 25 and jumps down the column ten at a time, landing on 35 and 45. The number 45 is circled.

Words to know

tens:

Groups of ten. 3 tens make 30.

ones:

Single things that are not in a group of ten.

hundred square:

The numbers 1 to 100 in rows of 10.

number bond:

Two numbers that make a total, like 7 and 3 make 10.

double:

The same number added twice, like 4 + 4.

exchange:

Swap 10 ones for 1 ten, or 1 ten for 10 ones.