kitchen table math, the sequel: paint by the numbers

## Monday, August 30, 2010

### paint by the numbers

1. C. and his friend E. take the online CollegeBoard SAT test first thing so we can get a baseline.

2. I attempt to score their tests and discover that the posted answer key apparently belongs to a different test.

3. I spend my commute time to and from the city working through the test myself.

4. After dinner I while away my evening capturing screen grabs of problems to post here in hopes that people will have time to confirm my solutions.

5. I stumble upon the actual answer key.

This isn't working.

Daniel Ethier said...

The triangle DFH has an area of 10 and consists of 4 small triangles. So each of them is 2.5. You could just multiply 25 by 2.5 and get 62.5

Or, notice that you can find a total of 4 triangles the same size as DFH making up most of triangle AFK, for an area of 40, leaving the bottom row of 9 small triangles. Since 8 small triangles is the same as two of triangle DFH, that's 20 more, leaving one small triangle, so add 2.5 more for a total again of 62.5

Anonymous said...

Or, to put it algebraically:

10/4 = x/25

Allison said...

Practice asking yourself what you know and what you need to know in common terms.

You are told you have 25 congruent little triangles. That means they are all the same. Then you're told something about a bigger triangle, but you're asked what is the area of a different big triangle. So go back to thinking about the little triangles.

In terms of little triangles, you're asked what is the area of 25 of them. In terms of little triangles, you're told the area of 4 of them. If you had that, would you have known what to do?

CassyT said...

Oh man, (hitting forehead) you can even figure it out based on what you know about units in a bar model drawing:
4 units = 10
1 unit = 10/4
25 units = 25 x 10/4