3.1 Teachers often ask children to share their strategies for solving problems with the class.  Read the following student answers and indicate whether each makes sense to you. Then, click on the button at the bottom of the page to continue.
 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   Written on paper 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." Does Carlos's reasoning make sense to you? Yes    No Does Henry's reasoning make sense to you? Yes    No Does Elliott's reasoning make sense to you? Yes    No Would you like to see a further explanation? Yes    No  Click here  to see a further explanation. Does Sarah's reasoning make sense to you? Yes    No

Maria
Manipulatives
 = 100 Called a flat = 10 Called a long = 1 Called a single

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.'

Does Maria's reasoning make sense to you?

Yes    No