Carlos 149 + 286
Written on paper
Henry 149 + 286
Henry says, "I know that 40 and 80 is 120, and one hundred and two hundred makes 300, and 120 and 300 is 420, and 9 and 6 is 14, so 420 and 10 is 430, and 4 more is 434."
Elliott 149 + 286
Sarah 149 + 286
Sarah says, "Well, 149 is only 1 away from 150, so 150 and 200 is 350, and 80 more is 430, and 6 more is 436. Then I have to subtract the 1, so it is 435."
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Maria Manipulatives
Maria uses manipulatives (base-ten blocks) to solve the problem. Maria says, "I took one flat for the 100 in 149 and 2 flats for the 200 in 286.
I took 12 longs: 4 for the 40 in 149 and 8 for the 80 in 286.
I took 15 singles for the 9 in 149 and the 6 in 286.
Then I counted like this, '100, 200, 300'; then for the longs, '310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 420'; then the singles, '421, 422, 423, 424, 425, 426, 427, 428, 429, 430, 431, 432, 433, 434, 435.'
So the answer is 435."
Does Maria's reasoning make sense to you?