options: Subtract multiples of 10 in the range 10-90 from multiples of 10 in the range 10-90 (positive or zero differences), using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method and explain the reasoning used.

Add within 100, including adding a two-digit number and a one-digit number, and adding a two-digit number and a multiple of 10, using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method and explain the reasoning used. Understand that in adding two-digit numbers, one adds tens and tens, ones and ones; and sometimes it is necessary to compose a ten.

Given a two-digit number, mentally find 10 more or 10 less than the number, without having to count; explain the reasoning used.
problem_activity: Stage 5: Add within 100 without Composing
Required Preparation
Materials to Gather
Paper clips
Two-color counters
Materials to Copy
Blackline Masters
Five in a Row Addition and Subtraction Stage 5 Gameboard

Narrative
Partner A chooses two numbers and places a paper clip on each number. They add the numbers and place a counter on the sum. Partner B moves one of the paper clips to a different number, adds the numbers, and places a counter on the sum. Students take turns moving one paper clip, finding the sum, and covering it with a counter.
Two gameboards are provided, one where students add a one-digit and a two-digit number and one where they add a two-digit and a two-digit number.
Additional Information
Each group of 2 needs 25 counters and 2 paperclips.


correct_option_index: 1