Math Is Fun Forum

mathxyz

Member

From: Brooklyn, NY

Registered: 2024-02-24

Posts: 1,053

Circular Swimming Pool

A circular swimming pool, 20 feet in diameter, is enclosed by a wooden deck that is 3 feet wide. What is the area of the deck? How much fence is required to enclose the deck?

Let me see.

A_d = area of deck.

A_d = area of big circle - area of little circle

Area of big circle = pi(r)^2

Let radius = 13 feet

Area of big circle = pi(13)^2 = 169pi.

Area of little circle = pi(10)^2 = 100pi.

A_d = 169pi -100pi

A_d = 69pi^2

Let C = circumference of enclosed deck.

C = pi•d, where d is diameter of big circle.

Let d = 3 feet + 20 feet + 3 feet.

C = 26pi feet.

Is any of this right?

Bob

Administrator

Registered: 2010-06-20

Posts: 10,627

Re: Circular Swimming Pool

The strict answer, based on the way you have worded that last sentence, is yes, some of it is right.

But let's go further. All of it is right! 

Bob

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

mathxyz

Member

From: Brooklyn, NY

Registered: 2024-02-24

Posts: 1,053

Re: Circular Swimming Pool

The strict answer, based on the way you have worded that last sentence, is yes, some of it is right.

But let's go further. All of it is right! 

Bob

Which part is right?

Which part is wrong?

Go further? I didn't answer the questions?

Bob

Administrator

Registered: 2010-06-20

Posts: 10,627

Re: Circular Swimming Pool

It was meant to be a joke.  There were two answers and both were right. But the question you asked was "Is any of this right?"

You have to remember I'm a teacher and we are notoriously pedantic.  'Any' could mean one part right and one part wrong so "Yes some of it is right" is the pedantic answer to your question. But that's not much help if what you really want to know is "Which bits are right and which are wrong?" Hence my next line "But let's go further. All of it is right!"

So no more to do as you've got all of it right.  Watch out of for the   That's the clue that 'teach' thinks he's being funny. Just humour me.

Bob

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

mathxyz

Member

From: Brooklyn, NY

Registered: 2024-02-24

Posts: 1,053

Re: Circular Swimming Pool

It was meant to be a joke.  There were two answers and both were right. But the question you asked was "Is any of this right?"

You have to remember I'm a teacher and we are notoriously pedantic.  'Any' could mean one part right and one part wrong so "Yes some of it is right" is the pedantic answer to your question. But that's not much help if what you really want to know is "Which bits are right and which are wrong?" Hence my next line "But let's go further. All of it is right!"

So no more to do as you've got all of it right.  Watch out of for the   That's the clue that 'teach' thinks he's being funny. Just humour me.

Bob

Ok. I get it now.