Counting Forward to 100 - First Grade Mathematics
Reaching one hundred is one of the greatest milestones in first grade mathematics. One hundred is a large, exciting quantity: it is ten whole bundles of ten, or one hundred single units gathered together. When you count to 100, you will travel through ten distinct number families, discovering how each decade builds smoothly upon the last. In this chapter, you will master the full sequence of numbers up to 100, navigate the tricky transitions between decades, and discover the elegant patterns hidden within the hundreds grid.
The Full Sequence of Decades to 100
Just like stepping stones across a wide river, the decade numbers guide your path all the way to 100.
The Ten Decades to 100:
10 -> Ten (1 Ten)
20 -> Twenty (2 Tens)
30 -> Thirty (3 Tens)
40 -> Forty (4 Tens)
50 -> Fifty (5 Tens)
60 -> Sixty (6 Tens)
70 -> Seventy (7 Tens)
80 -> Eighty (8 Tens)
90 -> Ninety (9 Tens)
100 -> One Hundred (10 Tens!)
The "-ty" Suffix Means Tens
Notice the word ending "-ty" in twenty, thirty, forty, fifty, sixty, seventy, eighty, and ninety. That syllable "-ty" comes from an old word meaning "tens." So sixty literally means "six tens," and eighty means "eight tens."
One Hundred: Ten Groups of Ten
When you have nine groups of ten (90) and you add one more group of ten, you have ten tens. We give this giant collection a brand-new name: one hundred (100). The numeral 100 has three digits: a 1 in the hundreds place, a 0 in the tens place, and a 0 in the ones place.
Navigating the Decades from 50 to 100
Let us explore the higher number families that live between 50 and 100.
Decade Transitions:
... 58, 59 -> [ 60 ] (Sixty)
... 68, 69 -> [ 70 ] (Seventy)
... 78, 79 -> [ 80 ] (Eighty)
... 88, 89 -> [ 90 ] (Ninety)
... 98, 99 -> [ 100 ] (ONE HUNDRED!)
The Sixties and Seventies
The sixties begin with 60 and end with 69. The seventies begin with 70 and end with 79. Pay close attention to pronunciation: say "sixteen" and "sixty" clearly so others know whether you mean 16 or 60.
The Eighties and Nineties
The eighties run from 80 to 89, and the nineties run from 90 to 99. When you reach 99, you have the greatest two-digit number possible. Adding just one more unit brings you to the monumental three-digit number: 100!
Finding Patterns on the 100 Chart
A 100 chart has 10 rows and 10 columns, containing all numbers from 1 to 100 in perfect order.
Corner of a 100 Chart:
Row 8: 71 72 73 74 75 76 77 78 79 80
Row 9: 81 82 83 84 85 86 87 88 89 90
Row 10: 91 92 93 94 95 96 97 98 99 100
The Magic of the Rightmost Column
Look down the far right column of a 100 chart. Every single number ends in zero: 10, 20, 30, 40, 50, 60, 70, 80, 90, 100. This is the column of pure tens!
Practice Exercises
Exercise 1: What number comes right after 69? What number comes right after 79? What number comes right after 89? What number comes right after 99?
Exercise 2: Write out the sequence of numbers starting at 87 and ending at 93.
Exercise 3: How many groups of ten are needed to make the number 100?
Exercise 4: Explain why the number 100 has three digits, while the number 99 has only two digits.
Solutions and Explanations
Solution to Exercise 1: The number right after 69 is 70. The number right after 79 is 80. The number right after 89 is 90. The number right after 99 is 100.
Solution to Exercise 2: The sequence of numbers from 87 to 93 is: 87, 88, 89, 90, 91, 92, 93.
Solution to Exercise 3: It takes exactly 10 groups of ten to make 100 (10 tens = 100).
Solution to Exercise 4: The number 99 has two digits because it is made of 9 tens and 9 ones (the highest two-digit number). When one more is added, you form a new place value: 1 hundred, 0 tens, and 0 ones, which is written with three digits as 100.