A question about surface area

[elcatracho]

This question is very hard for me because it does not deal with actual numbers, rather is deals with variables.
The question is... Find the surface area of a box of height h whose base dimensions are p and q and that satisfies the following condition
question A- The box is closed
Question B- The box has an open top
Question C- The box has an open top and a square base
I'd be really thankful for some assitance on this question. Thanks, Luis

 

[tkhunny]

This question is very hard for me because it does not deal with actual numbers, rather is deals with variables.
The question is... Find the surface area of a box of height h whose base dimensions are p and q and that satisfies the following condition
question A- The box is closed
Question B- The box has an open top
Question C- The box has an open top and a square base
I'd be really thankful for some assitance on this question. Thanks, Luis

Why does it make any difference? The concept of substitution is very, very VERY important. If x = 2, does it matter if you write 2 or x? No. They are the same.

How would you work this problem? Just set it up. Don't solve it.

Find the surface area of a box of height 12 in whose base dimensions are 6 in and 9 in and that satisfies the following condition
question A- The box is closed
Question B- The box has an open top
Question C- The box has an open top and a square base

I'll do the first one. Top and bottom are the same, 2*6*9. Two sides match, 2*6*12. The other two sides also match, 2*9*12.

 

[elcatracho]

I understand the first part because it follows the Surface area formula... the problem that i'm running into is the fact that i don't understand how having the top open will affect the surface area. Will it just be adding another p*q because their is an additional space that is exposed and that would be it's area. And for step three how would I be able to express that the bottom is a sqaure? by simply stating that p=q? I think I have an idea of how to solve it but i'm still a bit confused. Thanks, Luis

 

[Denis]

I understand the first part because it follows the Surface area formula... the problem that i'm running into is the fact that i don't understand how having the top open will affect the surface area. Will it just be adding another p*q because their is an additional space that is exposed and that would be it's area.

C'mon Luis...THINK!
A box with a top has 6 "surfaces", the top being one (equal to bottom);
a box with no top has 5 surfaces...THERE'S NO TOP!

 

[elcatracho]

help

I'm still confused because wouldn't a box with an OPEN top have seven sides since there is a new side exposed. WOuld u just write it as... 2pq+2ph+2Qh+ pq. The last part of the question still has me confused but i think I understand the second part I just want to make sure I understand it. Please I just want to put this problem to rest. Thanks, Luis

 

[Denis]

Re: help

I'm still confused because wouldn't a box with an OPEN top have seven sides since there is a new side exposed. WOuld u just write it as... 2pq+2ph+2Qh+ pq. The last part of the question still has me confused but i think I understand the second part I just want to make sure I understand it. Please I just want to put this problem to rest. Thanks, Luis

No Luis; an "open top" means NO TOP whatsoever:
like a square coffee cup or something

Say you paint a no top box: 5 surfaces, right?
But paint a box with a top: 6 surfaces, right?