Standard deviation question. fan and medal!
At a fair, tickets are sold to play games and ride rides. The ticket sales per person are normally distributed as shown below (picture attached).

What percentage of people bought 100 tickets or more?
A. 35%
B. 84%
C. 16%
D. 66%

Question

Standard deviation question. fan and medal!
At a fair, tickets are sold to play games and ride rides. The ticket sales per person are normally distributed as shown below (picture attached).

What percentage of people bought 100 tickets or more?
	A.  	35%
	B.  	84%
	C.  	16%
	D.  	66%

anonymous · Answer

attachment

anonymous · Answer

@campbell_st hey i am so sorry if i'm bothering you but i am seriously so desperate and confused, >.< any idea? I am leaning towards 16% and 35%

campbell_st · Answer

100 tickets looks to be 1 standard deviation above the mean... 

so the area between 1 SD below and 1SD above is approx 68%  given its symmetic about the mean... have it, so you choice makes sense

anonymous · Answer

Okay, I know that from the right and left of 100 is 50%. Wouldn't it decrease from there? Here is how I'm finding this: @campbell_st

anonymous · Answer

Sorry not 100, 80. From the right and left of 80.

campbell_st · Answer

ok... so looking at your original curve the mean is 80... its the centre of a symmetrical curve. 

the standard deviation appears to be 20... since the scale is 

20 40 60 80 100 120 140

then its just a case of knowing the basic percentages

anonymous · Answer

The basic percentages are what I don't know.

campbell_st · Answer

so 100 tickets or more is 50% - the 34% for 1 standard deviation above the mean...

anonymous · Answer

Okay, so here is what I know. How do I figure out the percentages below 50%?

anonymous · Answer

Okay! I think it's 16%. Here's why:

anonymous · Answer

@SolomonZelman I apologize if I am bothering you but can you check my work as well? I want a second opinion.

amistre64 · Answer

something called an empirical rule of thumb gives approximations for area that are 1,2,3 sds from the mean.  the empirical rule should simply be put to memory is all

amistre64 · Answer

from -1 to 1 sds, 68% of the data falls within
from -2 to 2 sds, 95% of the data falls within
from -3 to 3 sds, 99% of the data falls within, some have this last one as a decimal

amistre64 · Answer

from the mean, we half those  so yeah:  50 - 34 gives us whats left from 1 to infinity sds

anonymous · Answer

Awesome!! Thank you so much for clarifying =) So yes: 16% ? 50-34=16

amistre64 · Answer

16 is reasonable to me yes

anonymous · Answer

Thank you!! Could you possibly check one more of my answers on a different problem?

anonymous · Answer

If not I understand :) @amistre64