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Math Help - Percentage and ratio using integers help

  1. #1
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    Percentage and ratio using integers help

    Currently studying mathematics for engineers third edition given i havnt done maths for about 9 years its not going to bad but im stuck on theses question

    The pressure in a vessel is increased by 12% to 130 nm calculate the original pressure now this is how i worked it out can someone please tell me where im going wrong

    12/ 100= 0.12x130= 15.6 this answer being the increase thus giving me 130- 15.6 =114.4 ( original value)

    But the answer in the book gives 116.07 where am i going wrong ?

    Next question

    Express the ratio 1 1/2 : 3 1/4 using only integers now this one i cannot figure out an integer is a whole number so how would i calculate this ?

    Any help appreciated
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  2. #2
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    Re: Percentage and ratio using integers help

    Let x be the original value. An increase in 12% means an additional 0.12x. Thus, an 12% in x means x + 0.12x = 1.12x.

    Then solve the equation 1.12x = 130. Rounding to the nearest hunderdth decimal point yields x = 116.07.

    What you did was 0.12 * 130 = 15.6 which means 12% of the new value. You want to find 12% of the original value and then subtract that from 130. The words in mathematical form yields x = 130 - 0.12x which yields x = 116.07.

    Second problem - According to the directions, I'm assuming they want a ratio of two integers like 1 : 2 or 3 : 5 and not a ratio of two fractions.

    1 1/2 = 1 + 1/2 = 1 + 0.5 = 1.5 = 1.5/1 = 1.5/1 * 10/10 = 15/10 = 3/2
    3 1/4 = 3 + 1/4 = 3 + 0.25 = 3.25 = 3.25/1 = 3.25 * 100/100 = 325/100 = 13/4

    1 1/2 : 3 1/4 = (3/2) : (13/4) = (3/2) / (13/4) = (3/2) * (4/13) = 12/26 = 6/13 = 6 : 13
    Last edited by mathguy25; May 1st 2013 at 07:19 AM.
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  3. #3
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    Re: Percentage and ratio using integers help

    Thanks for the help.much appreciated
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