# Thread: How to use the PI function? (Excel 2000 SP3)

1. ## How to use the PI function? (Excel 2000 SP3)

Sorry I know this is the basic but so am I. How do I solve this problem:

Local Pizza parlor sells pizza at \$1 per inch. The pizza slice is \$1 for each inch in diameter. For example: a 5" wide pizza is \$5, a 10" wide pizza costs \$10.

For each budget below, deterime which choice will buy you more pizza.

1) You have \$15. Should you buy three 5" wide pizzas OR one 15" wide pizza?
2) You have \$20. Should you buy two 10" wide pizzas OR one 20" wide pizza?

Use the function for

2. ## Re: How to use the PI function? (Excel 2000 SP3)

Hans, yes this is an assignment. Sorry should have input this and added that just point me in the right start /direction as I will never learn without being "hands on". But, I have been working on this for 2 days and have looked again in Woody's Office 2000 Special Edition book but found no PI description and Excel help is of no use so I finally decided on posting. Thanks for 'reading between the lines' and NOT solving the entire problem but giving me a starting point! Going to Excel now to figure it out with your starting points.

Thanks again,
Robert

3. ## Re: How to use the PI function? (Excel 2000 SP3)

I just do not get this! I'm just not grasping the question. What does the numbers in column B (Area) stand for. So, to answer the 1st question for which is a better deal, just multiply B2 * 3 and if it's lower than B4 than that is a better deal? To me, what's the difference if three 5" pizzas is \$15 or one 15" pizza is \$15 aren't they both the same? You get the same amount of pizza for the same amount of money? But, probably not. That's what I mean by I just don't get the question itself?????? Math not my best subject!

Robert

4. ## Re: How to use the PI function? (Excel 2000 SP3)

1) Hans made a mistake in his formula. it should be for B2:
=+PI()*(A2/2)^2

Since A2 is the DIAMETER. A2/2 is the radius.

2) To answer your question: Yes 3x5" pizzas are \$15 and 1 15" pizza is \$15.
BUT,What is the area of 3 x 5" pizzas (you are right it is 3*b2) compared to the area of the 15" pizza (b4)? For that \$15 which one gives you more pizza (hint: it's the one with the greater area)?

The same logic applies in question 2: what is the area of 2 x 10" pizzas compared to 1 20" pizza (both are \$20)? which one gives more pizza (has greater area)?

Steve

5. ## Re: How to use the PI function? (Excel 2000 SP3)

Trying to let the Lounge do your homework assignment for you? <img src=/S/grin.gif border=0 alt=grin width=15 height=15>

I'll give you some clues, but I think you should try to work out the problem yourself.

The area of a circle is PI * r^2 where r is the radius of the circle (pizza). The * symbol stands for multiplication and ^ means "to the power".
The radius of a circle is the distance from the center of the circle to its edge. In other words, it is half the diameter.

To get a feeling of how it works, make a little table. We'll start with headings: in a new, blank worksheet, enter the text Diameter in cell A1, and the text Area in cell B1.

In cell A2, enter the number 5, and in cell A3, enter the number 10.
In cell B2, enter the formula for the area of a circle with diameter in A2: =PI()*(A2/2)^2
Select cell B2. You will see a small black square in the lower right corner. This is called the fill grip. Drag this fill grip one cell down, then release the mouse button. If you do it correctly, Excel will copy the formula from cell B2 to cell B3. This is called "filling down". If you make a mistake, you can always Undo (Ctrl+Z).
Now, select the rectangular block from cell A2 to cell B3 (in Excel terminology, the range A2:B3).
Again, you will see a fill grip in the lower right corner of the selected area. Drag the fill grip down a few rows. You will see that the series in column A is continued with 15, 20, ... Column B contains the corresponding area.

Now, try to work out from looking at this little table which of the choices is better value-for-money.

6. ## Re: How to use the PI function? (Excel 2000 SP3)

Steve,

<img src=/S/blush.gif border=0 alt=blush width=15 height=15> Of course you're right about my mistake. I did think about the radius/2 bit, but I was rushed to post a reply and forgot about it. Thanks for pointing it out - I corrected my reply.

7. ## Re: How to use the PI function? (Excel 2000 SP3)

Completely understandable. Just didn't want to get Robert any more confused.

Steve

8. ## Re: How to use the PI function? (Excel 2000 SP3)

Thanks Steve for the slight mistake in Hans' formula and the simple explanations. I have finished the comparisons and the chart but more importantly, I understand the WHY's! To me, if you just input the numbers without understanding them, you will never be able to replicate them when given a totally different scenario. Thank you Hans for the starting direction and again for not just doing the problem for me.

Maybe I will purchase Woody's Excel book if he has one as I obiviously need one. Support the site/newsletters too [img]/forums/images/smilies/smile.gif[/img]

Mahalo,
Robert

9. ## Re: How to use the PI function? (Excel 2000 SP3)

Another way to "see" teh problem/solution.

Make a circle 3" in diameter and make 2 x 1.5" in diameter and 3 x 1" in diameter. Now lay the 2 1.5" diam circles in the 3" and you can SEE how much more area there is. DO the same for the 3 x 1".

Steve

10. ## Re: How to use the PI function? (Excel 2000 SP3)

Robert,

following up on Steve's suggestion of drawing circles, which I was going to suggest before I saw his post, see the attached drawing. Sorry I couldn't get some actual pizzas (my clipart collection is messed up).

You can't actually see how much more area there is in the bigger pizza but you can certainly see the bigger pizza has MUCH more area than the 3 little pizzas, even tho they all have the same measure across.

Another thing to help you see the relationship of numbers is just to look at the formulas (the corrected one of course) for the area of a circle without worrying about actual numbers:
area=PI*((DIAMETER/2)^2)

So for the big pizza, the total area is
PI*((DIAMETER/2)^2) whatever the diameter is (the PI and 2 never change)

the area for a small pizza which has 1/3 the daimeter of the big pizza is:
PI*(((DIAMETER/2)/3)^2)
that is, whatever the daimeter is of the big pizza, the little pizza (assuming you're doing the exercise of 3 small pizzas vs 1 big pizza) has 1/3 the daimeter (that's why the (DIAMETER/2) is divided by 3

and the 3 small pizzas have a total area of
3*PI*(((DIAMETER/2)/3)^2)

Comparing 1 big and 3 pizzas:
big area=PI*((DIAMETER/2)^2)
big area=PI*(DIAMETER/2)*(DIAMETER/2)
(just expanding the square operation into multiplication)

and
small area=3*PI*(((DIAMETER/2)/3)^2)=3*PI*((DIAMETER/2)/3)*((DIAMETER/2)/3)

Putting all the numbers together:
big area=(PI/4)*(DIAMETER*DIAMETER)
small area=(PI/12)*(DIAMETER*DIAMETER)

Both areas have (DIAMETER*DIAMETER) so they don't matter in the comparison.

What's left is (PI/4) and (PI/12). (PI/4) is 3 times bigger than (PI/12) [that is any number divided by 4 is 3x bigger than same number divided by 12].

So, it doesn't matter what the radius/diameter of the pizzas are. If you take 3 small pizzas of the same sizes (diameter) and compare them to 1 big pizza with 3 times the diameter of the small one, the area of the big one will ALWAYS be 3 times the area of the 3 small ones combined.

So you should be able to amend your spreadsheet to show this.

And I'm going to lunch now.

Fred

PS: If you're in Hawaii, I wish I were there too again (just was there in Dec).

11. ## Re: How to use the PI function? (Excel 2000 SP3)

Thanks Fred for the detailed explanation. I figured out how to "grasp" the problem just the way Steve suggested because as you and everyone else could see, I thought that it didn't matter since 3-5" pizzas would be the same as 1-15" pizza as both would total 15". Not even close! Made it so much easier to understand the relationships. You're cell inputs differ from mine so will revist and see the difference (of course you are right) as the assignment clearly states that, "It should be amendable."

Again, thanks everyone for all your help.

Appreciative,
Robert

PS: Fred, don't know where you live but yeah Hawaii was gorgeous in Dec. compared to most other States. I'm leaving soon for 2 weeks in Brooklyn and "Turnaround is fair play"...I guess! [img]/forums/images/smilies/smile.gif[/img] LOL

12. ## Re: How to use the PI function? (Excel 2000 SP3)

Robert,

Your cell inputs (along with Hans's) are different from mine because I approached the problem in a general way of trying to find relationships of the pies. Hans solution was finding the areas of the pies. I don't want to attach my spreadsheet bcs, as Hans suggested, the Lounge is not a place to get your HW done. When you're done, I can send you my spreadsheet. It's not much different than what Hans walked you thru but mine is geared to showing the relationship. But you're on the honor system in telling me when the assignment is to be handed in, if you want me to send you mine work.

I live in NJ and it's been a cold winter. If you're going to Brooklyn NY (I think there are a few others around the country), that's where I grew up. I'd trade Brooklyn or NJ for Hawaii any day.

Fred

13. ## Re: How to use the PI function? (Excel 2000 SP3)

Yeah Fred it's NY. I helped my sister relocate from SF to Brooklyn last year. I've been tracking the weather but hey, my tickets are in hand so whatever. My sister used to live in NJ also. When I went to vist her years ago I liked it their. It was winter time also.

No need for the spreadsheet but I do appreciate the offer. I think I have it figured out and can do it both Hans and your way. I would never allows someone to do my work for me as when it comes down to the 'nitty gritty' and the 'chips are down', I will not be able to deliver. What's the sense then? All talk and no substance!

Bye the bye, played golf yesterday. No clouds. 80 degrees. No wind. No waiting between holes. 3 other friends. Sorry couldn't resist. LOL

See'ya,
Robert

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