Logic question


by Peter Pan
Tags: logic
Peter Pan
Peter Pan is offline
#1
Nov7-03, 03:18 PM
P: 44
This question is making me angry. I think I know the answer but I have some co-workers that disagree.

Q. Sally is the 50th best student in her class and the 50th worst. How many students are in her class?

A. 101, 100, 99, 50

I believe the anwser is 99
Phys.Org News Partner Science news on Phys.org
SensaBubble: It's a bubble, but not as we know it (w/ video)
The hemihelix: Scientists discover a new shape using rubber bands (w/ video)
Microbes provide insights into evolution of human language
Kerrie
Kerrie is offline
#2
Nov7-03, 03:35 PM
Emeritus
PF Gold
Kerrie's Avatar
P: 1,188
i think the answer is 50
Peter Pan
Peter Pan is offline
#3
Nov7-03, 03:46 PM
P: 44
I think 50 is the answer
Tell my how you came up with that. This is why I believe the answer is 99.

If sally is the 50th best student in her class, that means there are 49 student who are better. Also, if Sally is the 50th worst student, that means there are 49 that are worse than her

49 better + 49 worse + sally = 99

quartodeciman
quartodeciman is offline
#4
Nov7-03, 04:04 PM
P: 383

Logic question


Let's try something shorter. If Sally were 3rd best and also 3rd worst, the rankings would look like this:

best rank/worst rank/name

1st /5th /Cheryl
2nd /4th /Laura
3rd /3rd /Sally <---
4th /2nd /Anne
5th /1st /Betty

Note that 1st best simply means "the best" and 1st worst simply means "the worst".

There are 5, or 2(3)-1 class members. I don't think it makes any significant difference for 50th best and 50th worst. So, the number of members ought to be 2(50)-1 = 99, and you, Peter, are correct.

Of course, if some class members have equal rank, then more members are required.
NateTG
NateTG is offline
#5
Nov7-03, 04:35 PM
Sci Advisor
HW Helper
P: 2,538
Well, you also need to make sure there are no ties for 50th
Peter Pan
Peter Pan is offline
#6
Nov7-03, 04:54 PM
P: 44
Assume to ties
photon
photon is offline
#7
Nov22-03, 12:11 AM
P: 124
1st /5th /Cheryl
2nd /4th /Laura
3rd /3rd /Sally <---
4th /2nd /Anne
5th /1st /Betty
Seems like the answer has to be 99. There are no ties, and Sally is 3rd best and 3rd worst out of five. There are not 6 people in the group, but five because a number has to be odd to have a middle integer. 3 is Sally's rank. 3x2-1=5. So, for Peter Pans's question: 50 is Sally's rank. 50x2-1=99
The answer then, is 99.
EDIT: When I subtract 1, I am subtracting Sally.
Kerrie
Kerrie is offline
#8
Nov22-03, 06:25 AM
Emeritus
PF Gold
Kerrie's Avatar
P: 1,188
well the way i worked it out is 50th best would mean 49 people in front of her were better, and 49 people in front of her were worse...so that's how i came up with a total of 50...but 99 also makes sense...
Mentat
Mentat is offline
#9
Nov22-03, 10:16 AM
P: 3,715
Originally posted by Kerrie
well the way i worked it out is 50th best would mean 49 people in front of her were better, and 49 people in front of her were worse...so that's how i came up with a total of 50...but 99 also makes sense...
Yes, 49 people in front of her were better, but 50 plus 49 is 99.
stevenson
stevenson is offline
#10
Dec11-03, 07:02 AM
stevenson's Avatar
P: 3
If she's the 50th best that would mean she's number 50 from the top.
If she's the 50th worst that would also mean she's the 50th from the
top. Both are saying the same exact thing but they are worded different, really simple. Thanks [:D]
Peter Pan
Peter Pan is offline
#11
Dec11-03, 02:19 PM
P: 44
"If she's the 50th best that would mean she's number 50 from the top.
If she's the 50th worst that would also mean she's the 50th from the
top. Both are saying the same exact thing but they are worded different, really simple."

What is your point?
diverz
diverz is offline
#12
Dec12-03, 01:54 AM
P: 16
Theres no additional information to determine the number of students in Sally's class.

The statement you gave merely states that Sally is in the 50th position.
Peter Pan
Peter Pan is offline
#13
Dec12-03, 11:49 AM
P: 44
Theres no additional information to determine the number of students in Sally's class.
I disagree. The question states that sally is both the 50th best and worst student in her class.

50th best implies that 49 students have done better.
50th worst implies that 49 students have done worst.
fffbone
fffbone is offline
#14
Dec29-03, 08:50 AM
fffbone's Avatar
P: 33
The statement simply implies that there are 49 students better than sally and 49 students worse, so the minimum number of students in her class in 99. As there can be infinite many students having the same grade as her, there can be infinte many students in tie for the 50th place. Thus the number of students in her class can be any of the natural numbers that is greater than or equal to 99.
Adam
Adam is offline
#15
Dec29-03, 09:11 AM
P: 454
As someone said, 99. As someone else said, you must make sure there are no ties. Also, there is the option that all people got the same score.


Register to reply

Related Discussions
question on fuzy logic Precalculus Mathematics Homework 1
Logic Question! General Math 4
Logic Question Calculus & Beyond Homework 1
Logic question Biology, Chemistry & Other Homework 0
Propositional Logic Question Engineering, Comp Sci, & Technology Homework 0