Unit 5, Lesson 3

Add It, Explain It

Grade 1

Warm-up

Find the value of each expression mentally.

Activity 1

Lin and Han are both finding the value of .
Look at how each student started.
What should they do next to find the value?
Write equations to represent your thinking.

Lin started by putting 3 tens and 5 tens together.
She recorded her first step like this: .
Han started with 54 and added 3 tens.
He recorded his first step like this: .

Activity 2

Find the value of using Lin’s or Han’s method.
Show your thinking using equations.

Student Section Summary

We added numbers within 100.

We learned different methods to add by thinking about tens and ones and record our thinking with equations.

Add on tens then ones:

Base ten diagram, 3 groups with numbers below. First group, 2 tens 3 ones, below 23. Second group, 4 tens, below 63. Third group, 5 ones, below 68.

Add tens and tens and ones and ones:

Base ten diagram. Group of tens, 2 tens, 4 tens, labeled 60. Group of ones, 3 ones, 5 ones, labeled 8.

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