P
B * R
P = Portion (part of the
whole)
B = Base (the total, or the whole thing)
R = Rate (decimal, or a percentage)
Cover the piece you are
trying to calculate, and do the math on the pieces that remain.
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Example 1: I want to find the percentage (rate) that sales
of widgets contributed to my total sales.
I know the portion (the
widget sales) and the base (the total sales)
I'm trying to calculate
the rate.
Cover the R, and the math
that remains is:
P
B
If I sold 75 widgets and had total
sales of 150 items, the math is:
75
150
Answer: .50, or 50%
50% of my total sales were
widgets
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Example 2: I know the total, and I know the percentage a
particular item contributed, but I want to know the number sold of
that item.
I sold 150 items; 40%
(.40) were widgets. How many widgets did I sell?
I am trying to calculate
the portion. Cover the P and the math that remains is:
B*R
Answer: 150 * .40 = 60
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Example 3: I know that I sold 70 widgets, and that widgets
represent 25% (.25) of my total sales. What were my total sales?
I am trying to calculate
the base. Cover the B and the math that remains is:
P
R
Answer: 70/.25 = 280
I had total sales of 280
units.
Finding a Percentage of Change
This year I sold 100 units. Last
year I sold 80 units. By what percentage did my sales increase?
First, you must calculate the change
in units:
This year - Last Year
100 - 80 = 20 units difference
Next, I divide the change
in units by last year's number.
20/80 = .25 (25%)
There has been a 25%
increase in sales between last year and this year. I can check my work
by multiplying last year's sales by the increase, and adding that
amount to last year's sales.
80 * .25 = 20
80+20 = 100
or, the shortcut:
80 *1.25 = 100
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