Lesson 2.3 · Place Value to 1,000
Skip counting by 5s, 10s and 100s
Counting one at a time up to 500 would take forever. Skip counting is faster. You jump by the same amount each time, like 5, 10 or 100.
Count by 5s
Start at 0 and jump by 5 each time.
0, 5, 10, 15, 20, 25, 30, … When you count by 5s from 0, the ones digit goes 0, 5, 0, 5 over and over.
Count by 10s
When you count by 10s, the tens digit goes up by 1 each time. The ones digit stays the same.
- 10, 20, 30, 40, 50
- 230, 240, 250, 260, 270
When the tens reach 9, the next jump goes up to a new hundred: 180, 190, 200.
Count by 100s
When you count by 100s, the hundreds digit goes up by 1. The tens and ones stay the same.
- 100, 200, 300, …, 900, 1,000
- 150, 250, 350, 450
Watch one digit change
Skip counting by 10 changes the tens digit. Skip counting by 100 changes the hundreds digit. The other digits stay the same.
Worked example: Count by 5s
Count by 5s: 35, 40, 45, ___, ___.
Add 5 each time. 45 and 5 more is 50. 50 and 5 more is 55. The missing numbers are 50 and 55.
Worked example: Count by 10s past a hundred
Count by 10s: 370, 380, 390, ___.
The tens digit is already 9. One more ten makes a new hundred. The next number is 400.
Worked example: Count by 100s from a middle number
Count by 100s: 425, 525, 625, ___.
Only the hundreds digit changes. 6 hundreds becomes 7 hundreds. The next number is 725.
Common mistake
After 390, counting by 10s does not go to 3100. Ten tens make a hundred, so 390 and 10 more is 400.
Tip
Count by 5s using the fingers on your hands: each hand is 5.
Practice
Count by 5s: 15, 20, 25, ___.
Type a number.
Count by 10s: 130, 140, 150, ___.
Type a number.
Count by 100s: 500, 600, 700, ___.
Type a number.
Count by 10s: 270, 280, 290, ___.
Type a number.
Count by 100s: 348, 448, 548, ___.
Type a number.
Which list counts by 5s?
Nine friends each hold up one hand. Count the fingers by 5s. How many fingers are there?
Type a number.
Count by 100s: 700, 800, 900, ___.
Type a number.