What is the surface area of a rectangular prism with a length of 3 mm, a width of 5 mm, and a height of 8 mm?

________mm2 158?

Question

What is the surface area of a rectangular prism with a length of 3 mm, a width of 5 mm, and a height of 8 mm?

________mm2          158?

masterdestroyer55 · Answer

@imqwerty @dayakar @mathstudent55

masterdestroyer55 · Answer

@Qwertty123

masterdestroyer55 · Answer

@King.Void.

ltrout · Answer

Do you know how to find surface area?

masterdestroyer55 · Answer

yes. add them all up then divide by 3?

ltrout · Answer

The formula is $$A = 2(wl + hl + hw)$$

masterdestroyer55 · Answer

so then A = 158?

ltrout · Answer

One sec let me get a calculator lol

masterdestroyer55 · Answer

A=2(wl+hl+hw)=2·(5·3+8·3+8·5)=158       is it correct?

ltrout · Answer

Yes that's correct :)

ltrout · Answer

Sorry still too early for me to be doing math in my head

masterdestroyer55 · Answer

ok i got confused, because the last question i had, the answer was also 158.   i just wanted to make sure

masterdestroyer55 · Answer

i have more, but im going to open a new question first.

mathstudent55 · Answer

Correct.
Another way:
Lateral area = perimeter of the base * height
Base area = 2 * length * width of the base

LA = (3 + 3 + 5 + 5)mm * 8 mm = 128 mm^2
BA = 2 * 3 mm * 5 mm = 30 mm^2

Total surface area = LA + BA = 128 mm^2 + 30 mm^2 = 158 mm^2

ltrout · Answer

Which would you say is quicker @mathstudent55

mathstudent55 · Answer

I explained each step which makes it longer. 

Here it is in a quicker one-line expression: 
SA = Ph + 2lw = (3 + 3 + 5 + 5)8 + 2 * 3 * 5 = 158 

I think that your method is still quicker, but there are occasions in which you are asked for just the lateral area, so it is also good to know how to find the lateral area.