1
Pulling a number apart
Discover Mathematics P2: Term 1, Lessons 21–30
GoalWrite a three-digit number as hundreds plus tens plus ones.
New words
expanded form · a number written as a sum of its place values, like 300 + 50 + 2place value · what a digit is worth in its placesum · the answer when we add
Explanation
We can pull a number apart into its place values. The number 352 has 3 hundreds, 5 tens and 2 ones. So 352 = 300 + 50 + 2. This is called expanded form. Each part is the value of one digit. To put the number back together, add the parts: 300 + 50 + 2 = 352.
Worked examples
241 has 2 hundreds, 4 tens and 1 one. In expanded form: 241 = 200 + 40 + 1.
705 has 7 hundreds, 0 tens and 5 ones. There are no tens, so 705 = 700 + 5.
To put it back together: 500 + 60 = 560.
Class activity
Pull apart your house number or phone-number groups. Take any three-digit number you see, such as 245, and say its parts aloud: 200, 40 and 5. Then say them in the other direction: 200 + 40 + 5 is 245.
Practice
1
Write 618 in expanded form.
600 + 10 + 8
2
Which number is 400 + 20 + 9?
429
3
Write 803 in expanded form.
800 + 3
4
Which number is 500 + 70?
570
5
The blocks show a number. Write it in expanded form.
300 + 40 + 6