2
Review: tens and ones
Discover Mathematics: Chapters 1–7
GoalRead, write and build numbers up to 100 as tens and ones, and count by tens.
New words
tens · full groups of tenones · single things left overdigit · one of the signs 0 to 9hundred · ten tens
Explanation
Every number up to 100 is made of tens and ones. The first digit tells the tens and the last digit tells the ones. The number 64 is 6 tens and 4 ones. One more than 59 is 60, because the ones make a new ten. We can also count by tens: 10, 20, 30, up to 100. Ten tens make one hundred.
Worked examples
Seif counts 26 flowers: 2 tens and 6 ones.
Tamer builds a number with 5 sticks and 8 cubes. He writes 58.
Seven sticks are seven tens, so the number is 70.
Class activity
Number building. Use small rolls of paper for tens and beans for ones. Ask the child to build 23, then 38, then 45. Then build a number yourself and ask the child to name it. Finish by counting by tens as high as you can.
Practice
1
Which number do the sticks and cubes show?
72
2
How many tens and ones are in 57?
5 tens and 7 ones
3
How many stars are there?
33
4
Count by tens: 30, 40, 50, __. What comes next?
60
5
What number comes just before 60?
59