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Letter b:Write the formula for the mean cell phone bill…. Answer all of them please

Letter b:Write the formula for the mean cell phone bill…. Answer all of them please-example-1
User Nick Kohrn
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1 Answer

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Explanation:

I could not find a way to write sigma as the capital Greek letter (and with the index indications on the top and the bottom).

so, I will simply write it like

sigma n=1 to 12 (xn)

when saying sum up all xn for n = 1 to 12.

I hope this is understandable.

m = the mean cell phone bill for the indicated period.

(a)

the whole year means all 12 months (from 1 to 12).

m = (sigma n=1 to 12 (xn))/12 =

= (83+86+78+82+95+87+90+76+88+82+83+71)/12 =

= 83.41666666... ≈ $83.42

(b)

the last 6 months are the months 7..12.

m = (sigma n=7 to 12 (xn))/6 =

= (90+76+88+82+83+71)/6 =

= 81.66666666... ≈ $81.67

(c)

from March to September are the months 3..9 (7 months).

m = (sigma n=3 to 9 (xn))/7 =

= (78+82+95+87+90+76+88)/7 =

= 85.14285714... ≈ $85.14

(d)

by looking through the list, clearly the 3 consecutive bills with the highest mean are May, June, July with $95, $87, $90.

why ? $95 and $90 are the highest bills anyway, and $87 is only $1 less than the third highest bill $88.

all other groups of 3 will have a lower sum than the mentioned 3. and therefore also their mean value will be lower (as this is just a division by the constant 3).

m = (sigma n=5 to 7 (xn))/3 =

= (95+87+90)/3 =

= 90.66666666... ≈ $90.67

User Rehan Shah
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