Take the 2-minute tour ×
Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. It's 100% free, no registration required.

10 feet of common 2-inch-bore lead piping weighs 50 lb. What is the formula for the weight of x feet of such lead piping? --Sawyer, Mathematician's Delight

I am not sure about what I am asked to do here. It is known that $$10F*2=50$$ and I am asked to write it down as $$XF*2=W$$ or is it something else?

share|improve this question

2 Answers 2

up vote 3 down vote accepted

Let $W$ be the weight as a function of the length $L$. So you know that when $L= 10$ ft then $W = 50$ lb. We sometimes will write this as $W(10) = 50$.

Now if $10$ ft weighs $50$ lb, then what would $5$ ft weigh? Well, half of that, i.e. $25$ lb. What would $1$ foot weigh? Well, one tenth of that, i.e. $5$ lb.

So $1$ foot of pipe weighs $5$ lb. $2$ ft would weight the double of that. Can you find the formula now? (Note that the fact that the pipe is $2$ in thick doesn't matter.)

share|improve this answer

First of all, the 2 in the "2-inch-bore" is utterly irrelevant and has no place in any formula. Think of it as "10 feet of (whatever-you-want) weighs 50 pounds: $x$ feet weighs how many pounds?" You want a formula for "how many", and you want that formula to involve $x$.

share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.