A bakery charges $0.10 for a cookie that is 2 inches in diameter. If the price is proportional to the area, how much do they charge for an extra large cookie that is 10 inches in diameter? Assume that each cookie is shaped of a circle.

$ 0.50
$ 1.00
$ 2.50
$ 12.50

Question

A bakery charges $0.10  for a cookie that is 2 inches in diameter. If the price is proportional to the area, how much do they charge for an extra large cookie that is 10 inches in diameter? Assume that each cookie is shaped of a circle.

$ 0.50
$ 1.00
$ 2.50
$ 12.50

faman39 · Answer

@tkhunny  can you able to help me with this ?

tkhunny · Answer

Here's the important part: "If the price is proportional to the area"

Translate that Price = k*Area or just P = k*A.

After that, there MUST be some given information.

"$0.10  for a cookie that is 2 inches in diameter"

There it is.  Now what?

faman39 · Answer

2.50 ?

tkhunny · Answer

Don't do that.  You just went magically from a partially set up problem statement to a solution out of the air.  Show your work and think it through.

We have:
 P = k*A.
and
"$0.10  for a cookie that is 2 inches in diameter"

Thus: 0.10 = k*pi*(2/2)^2 = k(pi) ==> k = 1/(10pi)

Now what?

faman39 · Answer

I m kinda confuse, you are saying multiply 2 three times then divide with 10, right?

tkhunny · Answer

No.  You must read this problem very carefully.  You are given the DIAMETER, but the relationship is with the AREA.  You must convert.  Diameter/2 = Radius.  pi*Radius^2 = Area.  It was mean of the question writer to use '2', since there were already two '2's in the development.

faman39 · Answer

so 2 is it right?

faman39 · Answer

oh ok thank you @tkhunny  for helping, i will try another way

tkhunny · Answer

Once we ahve determiend 'k', we are nearly done.

k = 1/(10pi)

(1/10pi)*pi*(10/2)^2 = 25/10 = 2.50

faman39 · Answer

It should second one?

faman39 · Answer

i guess not

tkhunny · Answer

I don't understand the question.  You just made me work the whole problem.  It's 2.50.

faman39 · Answer

I am sorry i could not get on beginning for network prob, now i went from up, where explain all, now i got.  thanks so much @tkhunny !

faman39 · Answer

So sorry for troubling :( i m really terrible

tkhunny · Answer

No name calling!  Just spend the time it takes.  You'll get it.

faman39 · Answer

I am really sorry for everything :(

tkhunny · Answer

Read some material on "Direct Proportion".  It's not impossible to learn it.