# How many bags of gravel

#### PatriciaR

##### New member
I found equations and did the calculation but the answer did not make sense for the following question. The area to install pavers is 3 feet x 20 feet; it is recommended that there be a 4 inch depth for the gravel. The gravel comes in bags labeled 0.5 cubic feet. How many bags will i need? Thank you for your help.

#### pka

##### Elite Member
I found equations and did the calculation but the answer did not make sense for the following question. The area to install pavers is 3 feet x 20 feet; it is recommended that there be a 4 inch depth for the gravel. The gravel comes in bags labeled 0.5 cubic feet. How many bags will i need? Thank you for your help.

#### Denis

##### Senior Member
I found equations and did the calculation.....
What "equation" did you use?
What is the volume of a 4 by 5 by 6 box?

#### pka

##### Elite Member
What is the volume of a 4 by 5 by 6 box?
No it is not. The dimensions are $$\displaystyle (4\times 36\times 240)\text{in}^3$$
Each bag fills $$\displaystyle 0.5\times 12^3=864$$ SEE HERE cubic inches.

#### Dr.Peterson

##### Elite Member
I found equations and did the calculation but the answer did not make sense for the following question. The area to install pavers is 3 feet x 20 feet; it is recommended that there be a 4 inch depth for the gravel. The gravel comes in bags labeled 0.5 cubic feet. How many bags will i need? Thank you for your help.
I would probably convert 4 inches to feet, find the number of cubic feet needed, and from there find the number of bags.

If you had shown your calculations, and why you felt your answer didn't make sense, we could have immediately told you either that you are correct, or that you had made one of several likely errors (such as not converting, or converting something incorrectly).

#### Denis

##### Senior Member
No it is not. The dimensions are $$\displaystyle (4\times 36\times 240)\text{in}^3$$
Each bag fills $$\displaystyle 0.5\times 12^3=864$$ SEE HERE cubic inches.
Huh?...I simply wanted to see if Patricia knew the volume formula;
4 * 5 * 6 = 120 cu. units.

#### pka

##### Elite Member
Huh?...I simply wanted to see if Patricia knew the volume formula;
4 * 5 * 6 = 120 cu. units.
Denis, having seen your post over the years, I fully understand that you are well-meaning but you are not an academic. Had had you been, you would have realized that Patricia needed a way to understand the cubic units. Your saying to find the volume (4)(5)(6) implies that each of those numbers represent the same unit of measure. They do not in this problem and so it is a dumb mistake on your part. How in would do you think misleading Patricia can help her?

#### PatriciaR

##### New member
I thought you would prefer to start from scratch. It looks like you are asking to see how I arrived at my answer. Here is the calculation as I see it:

Bags of gravel: size of pathway area (inches): 36 x 180 x 4=25920;
convert cubic inches to cubic feet: 25920 x .000578704=15;
calculate number of bags (bag size is .5 cubic ft) : 15/.5=30 bags of gravel.

I was seeking confirmation that these were the correct steps to take and that someone else would arrive at the same answer or not. I was most unsure about having to convert linear to cubic inches. Rather than say the answer did not make sense I should have said I didn't like it. The bags are heavy and there are alot of them.

#### Subhotosh Khan

##### Super Moderator
Staff member
I thought you would prefer to start from scratch. It looks like you are asking to see how I arrived at my answer. Here is the calculation as I see it:

Bags of gravel: size of pathway area (inches): 36 x 180 x 4=25920;
convert cubic inches to cubic feet: 25920 x .000578704=15;
calculate number of bags (bag size is .5 cubic ft) : 15/.5=30 bags of gravel.

I was seeking confirmation that these were the correct steps to take and that someone else would arrive at the same answer or not. I was most unsure about having to convert linear to cubic inches. Rather than say the answer did not make sense I should have said I didn't like it. The bags are heavy and there are alot of them.
Your method is correct - however I think you made a small mistake. In your OP you had said that the path was 20' long ( =240") You have used 180" (= 15').

#### Dr.Peterson

##### Elite Member
I thought you would prefer to start from scratch. It looks like you are asking to see how I arrived at my answer. Here is the calculation as I see it:

Bags of gravel: size of pathway area (inches): 36 x 180 x 4=25920;
convert cubic inches to cubic feet: 25920 x .000578704=15;
calculate number of bags (bag size is .5 cubic ft) : 15/.5=30 bags of gravel.

I was seeking confirmation that these were the correct steps to take and that someone else would arrive at the same answer or not. I was most unsure about having to convert linear to cubic inches. Rather than say the answer did not make sense I should have said I didn't like it. The bags are heavy and there are a lot of them.
Doing the calculations in feet, we get 3 ft * 20 ft * 4 in = 3 ft * 20 ft * 1/3 ft = 20 ft^3; then (20 ft^3) / (0.5 ft^3/bag) = 40 bags. (Much easier conversion!)

I tend to be surprised by numbers like this, too! (Or is it not really a surprise if you have learned to expect a surprise?)

By the way, as you saw when you read our submission guidelines, our main purpose is to help students learn to solve problems themselves, so we want to see what they have already done. A problem like this one could either be real-life or a textbook problem, so we assume the latter, and don't give an answer initially. Even if you are doing this for real, we like to be able to say, "everything you did was right except for ____." Without seeing your work, we'd too likely instead show you a very different method that might make you think you were wrong.

#### Denis

##### Senior Member
Denis, having seen your post over the years, I fully understand that you are well-meaning but you are not an academic. Had had you been, you would have realized that Patricia needed a way to understand the cubic units. Your saying to find the volume (4)(5)(6) implies that each of those numbers represent the same unit of measure. They do not in this problem and so it is a dumb mistake on your part. How in would do you think misleading Patricia can help her?
Correct on ALL counts...feel better

Once more, my purpose was ONLY to "inform" Patricia that the formula
to obtain the volume of a "box" is L*W*H (since no work was shown....)

Btw, the problem itself is quite simple...