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Math Help - Help on Pecentages

  1. #1
    Newbie
    Joined
    Dec 2008
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    2

    Help on Pecentages

    Hi,

    I am looking for an easy formula to calculate the following ;

    There are several different fees for room bookings depending on time of year and room type.

    Tourist information take 10% of any fee from a successfull booking

    So, say the normal price for a room is 30 then I need to increase the room booking fee by the same amount that would give me 30 once the tourist information have taken their 10% fee.

    This seemed easy at first but then seemed to get harder once I tried to come up with a general formula

    30 + 10%
    30 + (0.1 * 30)
    30 + (3)
    33

    However if I charge 33 and tourist info take 10% thats

    33 - (33 x 0.1) = 33 - 3.3 = 29.70

    Somehow I lose 30p ?

    I have to factor in the 10% of the 10% ???

    Anyhelp appreciated!
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  2. #2
    Junior Member
    Joined
    Dec 2008
    Posts
    52
    First off: When you are adding 10% to the 30 you are getting 99% of the price, because 30 is only 90% of the full price, and 10% of 90% = 9%. 90% + 9% = 99%. That is why you are slightly off target!

    (1) You need to first say that 30 is 90%, as it is. When you receive your 30, you are only receiving 90% of the money, because the Tourist Information took 10%.

    (2) So you need to find and add an extra 10%, which you would do by diving the 90% by 9 as 90/9 = 10%. So 30 divided by 9 is 30/9, which is simplified to 10/3, which is 3.333333333....recurring.

    (3) Simply add this to your 30 and get 33.33. Now when you remove 10% you will remove 3.3333... and have your 90% again which is 30.
    Last edited by Bruce; December 8th 2008 at 11:19 AM.
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  3. #3
    Newbie
    Joined
    Dec 2008
    Posts
    2
    Thanks alot. As usual its the way you think about the problem that trips you up !!!
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