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A vending machine is designed to dispense 8 ounces of coffee

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Intern
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Joined: 06 Oct 2017
Posts: 1
A vending machine is designed to dispense 8 ounces of coffee [#permalink]

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New post 14 Nov 2017, 08:40
Here's another way to solve this problem by NOT multiplying values:

I did it by dividing 1,5/2= 0,75 in each direction (8,1 +/- 0,75), then substract 0,3 from 0,75 (+/- 0,75), so you get 0,45. Then, of the 12 amounts listed, 11 are within the range of 8,1 - 0,45 or 8,1 + 0,45.
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Joined: 26 Dec 2016
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Re: A vending machine is designed to dispense 8 ounces of coffee [#permalink]

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New post 13 Jan 2018, 14:14
Bunuel wrote:
7.51 8.22 7.86 8.36
8.09 7.83 8.30 8.01
7.73 8.25 7.96 8.53

A vending machine is designed to dispense 8 ounces of coffee into a cup. After a test that recorded the number of ounces of coffee in each of 1000 cups dispensed by the vending machine, the 12 listed amounts, in ounces, were selected from the data above. If the 1000 recorded amounts have a mean of 8.1 ounces and a standard deviation of 0.3 ounces, how many of the 12 listed amounts are within 1.5 standard deviation of the mean?

A. four
b. Six
c. Nine
d. Ten
e. Eleven



I tried to explain this here: https://gmatclub.com/forum/a-vending-ma ... ml#p812247

We are given that SD=0.3 and mean=8.1. Question: how many of the 12 listed amounts are within 1.5 standard deviation of the mean?

1.5 standard deviation equals to 1.5*SD=1.5*0.3=0.45, so "within 1.5 standard deviation of them mean" - means in the range {8.1-0.45; 8.1+0.45} = {7.65; 8.55}.

Hope it's clear.
[/quote][/quote]

I'm sorry, but this still doesn't make sense to me why you multiplied the standard deviations. With SD=0.3 then 1 deviation away would be 8.4 and with SD=1.5 it'd be 9.6. Where does the reasoning for multiplying both SD come from?
Re: A vending machine is designed to dispense 8 ounces of coffee   [#permalink] 13 Jan 2018, 14:14

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