HP 12C, Руководство пользователя

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Section 6: Statistics Functions 99
File name: HP 12c Pt Converted_user's guide_English_HDP0F123E02_080207 Page: 11 of 281
Printed Date: { 2007/8/2Dimension: 14.8 cm x 21 cm
Weighted Mean
You can compute the weighted mean of a set of numbers if you know the
corresponding weights of the items in question.
1. Press
f
CLEAR
²
.
2. Key in the value of the item and press
\
, then key in its weight and press
_
. Key in the second item’s value, press
\
, key in the second weight,
and press
_
. Continue until you have entered all the values of the items and
their corresponding weights. The rule for entering the data is “item
\
weight
_
.”
3. Press
g
to calculate the weighted mean of the items.
Example:
Suppose that you stop during a vacation drive to purchase gasoline at
four stations as follows: 15 gallons at $1.16 per gallon, 7 gallons at $1.24 per
gallon, 10 gallons at $1.20 per gallon, and 17 gallons at $1.18 per gallon. You
want to find the average cost per gallon of gasoline purchased. If you purchased
the same quantity at each station, you could determine the simple arithmetic
average or mean using the
gÖ
keys. But since you know the value of the item
(gasoline) and its corresponding weight (number of gallons purchased), use the
g
keys to find the weighted mean:
Keystrokes Display
f
CLEAR
² 0.00
Clears statistics registers.
1.16
\
15
_ 1.00
First item and weight.
1.24
\
7
_ 2.00
Second item and weight.
1.2
\
10
_ 3.00
Third item and weight.
1.18
\
17
_ 4.00
Fourth item and weight.
g
1.19
Weighted mean cost per gallon.
A procedure for calculating the standard deviation and standard error (as well as
the mean) of weighted or grouped data is included in the hp 12c platinum
Solutions Handbook .