PS/IS 686 | Brooklyn, NY

Math and MoMath in 302

In Math we have been revisiting addition and subtraction strategies. In third grade, we expect students to have a repertoire of strategies.  In class, we call this our “Addition Toolkit”, or our “Subtraction Toolkit”.  We expect students to “look to the numbers” before approaching a problem, and choose a strategy based on the numbers in the problem.

For example, you would probably solve these three problems using different strategies:


This problem invites you to “count up”, because the numbers are so  close together.  If you envision 299 and 301 on a number line, there is only a difference of 2.    299 +2=301


However, in this problem, you would not count up from 5 to 203. Rather, you would likely remove the 5 from 203. Many students would also move “to a landmark”, removing 3 first, then 2 more.

Example:          (203-3) – 2= 200 – 2 =198


In this problem, many students would look at the number 39, and think That’s close to 40!    Students would use a landmark, and then adjust.  120- 40= 80 , then add back the 1.  80+1=81

Our goal is for students to have many different strategies for addition and subtraction, and that students are able to use them flexibly. 

You can view the variety of addition and subtraction strategies below:




Last Thursday,  the third grade classes were visited by Bruce Bayly from the Museum of Math (MoMath). We spend a really fun hour together! First Mr. Bruce inflated balloons and twisted them into 2-D and 3-D shapes (tetrahedron and cube) while we considered the number of faces and corners each had. It turned out that addition, multiplication, and geometry are all connected!


Then we did a little exploration of the relationship between size and sound. We explored the sounds made by metal cylinders of different lengths when they’re dropped on the floor, and when they’re coated with rosin and rubbed with the fingers. The grand finale ‘instrument’ was a turkey baster. Did you know that if you fill a turkey baster part way with water and blow across the opening like a flute, it makes a sound – and that if you then squeeze the bulb to raise or lower the level of the water, the pitch changes? (Try it if you have one at home!)

Mr. Bruce also taught the children an interesting game called “Sprouts.” Ask your child to teach you!

Upcoming Dates:

Tuesday, November 14th- World Map Assessment

Wednesday, November 15- Trip to Prospect Park Zoo

Thursday, November 16th- Parent Teacher Conferences– Look out for sign up, coming soon!