Calculating percentages ???

Question

How do you calculate percentages. I took a math class on this back in high school but i just wanted a refresher now that im in college and i kinda of forgot how to do the calculations. For example:

If the price of an item were $49.50, what would be the actual price if it were 20 percent off ???

Answer 1

I read this wrong the first time... If $ 49.50 is the price (WITH the 20% discount), then to figure out the original cost (BEFORE the discount):

$ 49.50 = 80% of original cost (we'll call original cost X)
$ 49.50 = .80 (turn into decimal) X
(divide both sides by .80 to isolate the X)
X = $ 61.875 rounded to $ 61.88 - the original cost (BEFORE the discount)

Answer 2

To subtract a percentage:
49.50 - 20% = 49.50 * (1 - 20/100) = 49.50 * 0.8 = 39.60.
Similarly, to add a percentage:
49.50 + 20% = 49.50 * (1 + 20/100) = 49.50 * 1.2 = 59.40.

If you want the percentage amount itself:
49.50 * 20% = 49.50 * 20 /100 = 49.50 * 0.2 = 9.90.
You can then add that to or subtract it from the 49.50.

I prefer the method in the first paragraph because it is reversible. If you want to know what number gives 250 when 18% is added, it is:
250 / (1 + 18/100) = 250/1.18 = 211.86.
Similarly to find what number gives 250 when 18% is deducted:
250 / (1 - 18/100) = 250/0.72 = 347.22.

Hope that has helped.

Answer 3

to calculate a %, divide you % number by 100(move the decimal two places to the left) then multiply by the subject number

in your example,

49.50 is 80% of the total

I would do it fractionally, to get to 20% of the total, divide your 80% by 4

80/4=20
or
49.50/4 = 12.375

then add your 20% to the 80% or

49.5+12.375 = 61.875

the actual price is either 61.87, or 61.88, it depends on the store's rounding...

Answer 4

doing the example,

actual price - (20% of the actual price) = price after 20% off.
actual price - ((20/100) * actual price) = 49.50
actual price(1 - 20/100) = 49.50
actual price = 49.50/0.8 = 61.88

Answer 5

the final price is
49.50 - (0.2*49.50)