The Museum of Science in Boston has an exhibit in which metal balls drop down a chute, bounce around, and wind up in one of 21 bins. After 1000 balls have dropped, the heights within the bins clearly follow a bell shaped curve. If the standard deviation is 3 bins, approximately how many balls are in bins 1-7?

100

160

50

330

Can anyone please help me out with this?

Question

The Museum of Science in Boston has an exhibit in which metal balls drop down a chute, bounce around, and wind up in one of 21 bins. After 1000 balls have dropped, the heights within the bins clearly follow a bell shaped curve. If the standard deviation is 3 bins, approximately how many balls are in bins 1-7?

100

160

50

330

Can anyone please help me out with this?

anonymous · Answer

http://stattrek.com/online-calculator/normal.aspx

anonymous · Answer

$$0.09121\times 1000=91$$is my best guess, but i don't really know any statistics

mrnood · Answer

if you have 21 bins then the 'middle bin' is bin 11 (starting at 1)

So the 'mean' of this distribution is 11.

The SD is 3

so using the above calculator (or your own tables ) you get that the probability of a ball being in bin 7 or less is .091  (as @satellite73 has done for you)

Therefore from 1000 balls the number of balls is .91 x 1000.

This is just a slight expansion on the answer above...