## Reflection: Exit Tickets Using a Formula to Find the Surface Area of Prisms - Section 3: Lesson End

I noticed a trend.  Students that solved 2 and 4 often solved them differently.  For problem #2, most students relied on the surface area formula for a rectangular prism:  2lw + 2lh + 2wh.  They did not use the same formula to find the unknown dimension for the rectangular prism on problem 4.

The equation would look something like:

76 = 2*5*2 + 2 * 5 * x + 2 * 2 * x

76 = 20 + 10x + 4x

76 = 14x + 20

56 = 14x

4 = x

I'm guessing the idea of substituting the variable h with the variable x seemed strange to the students.  Instead the students found the area of the two known faces and then used arithmetic with some guess and check to solve for x.

Question #4
Exit Tickets: Question #4

# Using a Formula to Find the Surface Area of Prisms

Unit 6: Geometry
Lesson 17 of 37

## Big Idea: Students will use their knowledge of nets to help them find an algebraic way of finding the surface area

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Standards:
Subject(s):
Math, surface area, Geometry, formulas
50 minutes

### Grant Harris

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