## Thursday, October 1, 2009

### Math problems of the week: 2nd grade Investigations vs. Singapore Math

I. The entirety of the 2nd grade Investigations "Assessment: How Many More?" (session 2.6, "How Many Tens? How Many Ones?"), administered at the end of May:

1. Jake collects wizard stickers.
He has 46 wizard stickers.

How many more does he need to have 60?

a. Write an equation that represents the situation.

b. Solve the problem and show your work.

2. Sally has 76 marbles.

How many more marbles does Sally need to have 100 marbles?

a. Write an equation that represents the situation.

b. Solve the problem and show your work.

II. Two of the 15 problems in the second-to-last Review in 2nd grade Singapore Math, Primary Mathematics 2B (Standards Edition), p. 162:

9. There are 120 boys at a concert.
There are 85 more girls than boys.
19 girls and 16 girls wear glasses.
(a) How many girls are there at the concert?

(b) How many children are there altogether?

(c) How many children do not wear glasses?

13. Kelly has \$6.80.
She wants to buy a photo album that costs \$8.50.
How much more money does she need?

III. Extra Credit:

Compare the level of higher-level thinking involved in writing an equation that "represents" the situations described in the first problem set with the higher-level thinking involved in doing the multi-step problem and the three-digit problem in the second problem set.

Why does the first problem set, but not the second, explicitly require students to show their work?