Question

The area of the base of a prism is 21 cm2. The perimeter of the base is 20 cm. The height of the prism is 8 cm.

What is the surface area of the prism?

___ cm2

Answer 1

Well first, what have you figured out about the prism with the given information?

Answer 2

Nothing ;(

Answer 3

I think its a triangular prism though

Answer 4

It is not a triangular prism. It is a rectangular prism. We know this because of the area of the base. We have 21 for the area. What two numbers go into 21?

Answer 5

7 and 3

Answer 6

Exactly. So if 7 is our length and 3 is our width, what would the perimeter of the rectangle be?

Answer 7

21

Answer 8

Are you sure its not 20? Cause 2(7) + 2(3) should be 20.

Answer 9

oh lol i did 7*3 (bad at math)

Answer 10

Lol its fine, but now we have the base, the perimeter, and the height. All we have to do is plug them into the surface area formula to get the answer. Do you know the formula for the surface area?

Answer 11

No i dont

Answer 12

Well the formula is \[2*b+perimeter*height\] Can you plug in the values yourself?

Answer 13

2*21*20*8?

Answer 14

2*21+20*8 i mean

Answer 15

\[(2*21)+(20*8)\] Yep you got it. So what do you get?

Answer 16

Sorry back 202?

Answer 17

Yes, it would be 202. So that would be your answer. Do you understand the steps we used?

Answer 18

Yes I do can u help me with a few more

Answer 19

Sure, just tag me in the question and I'll help right away.