The purpose of this activity is to introduce students to a new unit, the hundred. Students used connecting cubes to make tens in grade 1 and used tens and ones to count to and represent numbers within 120.

In an earlier unit, students were introduced to base-ten blocks and used base-ten diagrams to represent sums and differences within 100. Students build on this understanding as they use blocks to represent a starting number (96) and add ones until they reach a total value of 100. As students discover they have 10 tens, monitor for language they use to describe the total value of the blocks and the connections they make to their previous work with ones, tens, and three-digit numbers (MP7).

• “Can you explain how your diagram represents Andre’s total value using the fewest number of blocks possible?”
• “Is there a way to represent the same amount without any ones?”

• Invite previously identified students to share how they know the value of Andre’s blocks is 100.
• “If Andre used the fewest number of blocks, how many tens did he use?” (He had 10 tens.)
• “What if Andre wanted to use the greatest number of blocks to show this number? What would he do?” (He’d decompose all the tens to use only ones. He’d use 100 ones.)
• “In this activity, you showed you know that 10 ones is the same as 1 ten. Just like 10 ones is the same as 1 ten, 10 tens is the same as 1 hundred.”
• “A hundred is a unit that is made up of 10 tens.”

The purpose of this activity is for students to make sense of 100 when represented as 100 ones, 10 tens, or 1 unit of a hundred with base-ten blocks or base-ten diagrams. Students compare different ways to describe 100 and connect the descriptions to base-ten diagrams (MP7). Students understand that a hundred is made up of 10 tens and can also be thought of as a unit of 100 ones.

• “How did you decide which statement matched each diagram?”
• “How are these diagrams the same? How are they different?”

• “How did you know which diagram showed the way Lin saw the blocks?” (Lin said she saw 1 hundred, so she was thinking about the whole thing as a unit.)
• Invite previously identified students to share how they represented .
• “How could you represent the 100 in the expression with the fewest blocks?” (I could use 1 hundred block.)