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Forties and fifties
Discover Mathematics: Chapter 7
GoalRead and write 40 to 59, and count by tens up to 100.
New words
forty · four tensfifty · five tenshundred · ten tenscount by tens · say 10, 20, 30 and on
Explanation
After 39 comes 40, which is four tens. The numbers 41 to 49 are four tens and some ones. After 49 comes a new ten, so we get 50, which is five tens. The numbers 51 to 59 are five tens and some ones. We can also count by tens all the way up: 10, 20, 30, 40, 50, 60, 70, 80, 90. After ninety comes one hundred, which is ten tens.
Worked examples
Yassin shows 52 with sticks and cubes: 5 sticks and 2 cubes.
Malak has 45 peaches in crates: 4 tens and 5 ones.
Ten sticks, each one a ten, make one hundred. We count by tens: 10, 20, 30, up to 100.
Class activity
Tens race. Make a path of 10 paper squares on the floor and write 10, 20, 30 up to 100 on them, one number on each. The child hops along the path and says each number. Then hide one square and ask which number is missing.
Practice
1
How many grapes are there?
48
2
What number comes after 49?
50
3
Write the number for 5 tens and 3 ones.
53
4
Which number do the sticks and cubes show?
56
5
Count by tens: 50, 60, __, 80. What is missing?
70