Dino

01-17-2008, 11:36 AM

My college algebra class started this last Tuesday. We went through 85 pages of review in about 20 minutes. It's been 18 years since I've studied any math.

I think the book is wrong for the last word problem in the review. Here it is, and I show how I approached it and the answer I got.

Are you paying too much for a large pizza?

Pizza is one of the most popular foods available today, and the take-out pizza has become a staple in today's hurried world. But are you paying too much for that large pizza you ordered? Pizza sizes are typically designated by their diameters. A pizza of diameter "d" inches has an area of

PI(d/2)**2. (A.K.A. "PI-r-squared")

Let's assume that the cost of a pizza is determined by its area. Suppose a pizza parlor charges $4.00 for a 10-inch pizza and $9.25 for a 15-inch pizza. Evaluate the area of each pizza to show the owner that he is overcharging you by $0.25 for the larger pizza.

So, simple enough it seems. I'll use 3.14159 for PI.

10" pizza area = 3.14159 * (10/2)**2 =

3.14159 * (5)**2 =

3.14159 * 25 = 78.53975 sq. inches.

78.53975 / $4.00 = $0.1963 per square inch cost.

15" pizza area = 3.14159 * (15/2)**2 =

3.14158 * (7.5)**2 =

3.14159 * 56.25 = 176.71443 sq. inches.

176.71443 / $9.25 = $0.1910 per square inch cost.

If the 15" pizza sells for less per sq. inch than the 10" pizza, I personally would have a hard time convincing the Red Baron he was charging $0.25 too much.

What am I missing here?

Todd

I think the book is wrong for the last word problem in the review. Here it is, and I show how I approached it and the answer I got.

Are you paying too much for a large pizza?

Pizza is one of the most popular foods available today, and the take-out pizza has become a staple in today's hurried world. But are you paying too much for that large pizza you ordered? Pizza sizes are typically designated by their diameters. A pizza of diameter "d" inches has an area of

PI(d/2)**2. (A.K.A. "PI-r-squared")

Let's assume that the cost of a pizza is determined by its area. Suppose a pizza parlor charges $4.00 for a 10-inch pizza and $9.25 for a 15-inch pizza. Evaluate the area of each pizza to show the owner that he is overcharging you by $0.25 for the larger pizza.

So, simple enough it seems. I'll use 3.14159 for PI.

10" pizza area = 3.14159 * (10/2)**2 =

3.14159 * (5)**2 =

3.14159 * 25 = 78.53975 sq. inches.

78.53975 / $4.00 = $0.1963 per square inch cost.

15" pizza area = 3.14159 * (15/2)**2 =

3.14158 * (7.5)**2 =

3.14159 * 56.25 = 176.71443 sq. inches.

176.71443 / $9.25 = $0.1910 per square inch cost.

If the 15" pizza sells for less per sq. inch than the 10" pizza, I personally would have a hard time convincing the Red Baron he was charging $0.25 too much.

What am I missing here?

Todd