View Full Version : Help please
TL3687
Sep 8, 2013, 12:58 PM
A globe is 41.142 feet in diameter. Find its exact circumference (distance around) and then approximate its circumference using 3.14 for pi.
Wondergirl
Sep 8, 2013, 01:00 PM
Do you know the formula for circumference of a circle?
TL3687
Sep 8, 2013, 01:13 PM
C=2*pie*r
Wondergirl
Sep 8, 2013, 01:17 PM
So, plug the numbers into the formula.
Circumference = 2 • π • radius = π • diameter
TL3687
Sep 8, 2013, 01:18 PM
But I don't know the radius only the diameter
Wondergirl
Sep 8, 2013, 01:22 PM
but i don't know the radius only the diameter
What is the relationship of the diameter to the radius?
44286
Also, Circumference = π • diameter
TL3687
Sep 8, 2013, 01:24 PM
So your saying that pie times 41.142 id the exact circumference?
Wondergirl
Sep 8, 2013, 01:27 PM
so your saying that pie times 41.142 id the exact circumference?
apple pie or cherry pie?
It's pi = 3.14.
Circumference = π • diameter
Circumference = 3.14 times the diameter
TL3687
Sep 8, 2013, 01:28 PM
Okay thank you
TL3687
Sep 8, 2013, 01:34 PM
So the circumference is 129.251404954
Wondergirl
Sep 8, 2013, 01:36 PM
Your instructions are: Find its exact circumference (distance around) and then approximate its circumference.
Wondergirl
Sep 8, 2013, 01:40 PM
so the circumference is 129.251404954
I didn't get that. I got 129.18588.
Just did it on an online calculator = 129.18588
ebaines
Sep 9, 2013, 05:51 AM
There are two parts to this. First part is to find its "exact"circumference. This part is a trick question - it's impossible to write it out exactly because pi is an irrational number of infinite length, so the "exact" answer would have an infinite number of digits. However, given the fact that you are give the diameter to five significant digits the "best" answer would also have five significant digits, or 129.25. Tacking on more digits than that gives a false sense of accuracy, given that you only know the diameter to 5 decimals.
The second part is to use an estimate of pi of 3.14. Judy gave an answer already, but the answer should be truncated to only 3 decimals given that the estimate of pi that was used is good to only three decimals. So 129 is the right answer.
Wondergirl
Sep 9, 2013, 05:54 AM
The second part is to use an estimate of pi of 3.14. Judy gave an answer already, but the answer should be truncated to only 3 decimals given that the estimate of pi that was used is good to only three decimals. So 129 is the right answer.
I'm not Judy, and he was told to use pi = 3.14. There are TWO parts to the answer.