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Question 747432: Today oil is $90.00 a barrel, which is 175% of the cost in 2000. What did oil cost a barrel in 2000?
Answer by mikeebsc(26)   (Show Source):
You can put this solution on YOUR website! I'm guessing your problem lies in calculating percentages and/or word problems. These are very easy and I will try and explain. A percent is simply a number * 100 (or a number moved 2 decimal places to the right). Knowing this, if you need to, write 175% as 175.00%, and convert it back to a "regular" number. If we got the % by moving the decimal 2 places to the right, to get it back to a regular number, we simply move it 2 places to the left. So
175.00% = 1.75
Let's work on translating English to math.
Now that we have 2 whole numbers the problem reads "Today oil is 90.00 a barrel, which is 1.75 of the cost in 2000".
Now we let x represent an unknown value (the cost in 2000) we are trying to solve for. If need be you can write the problem again as "Oil is 90 a barrel = 1.75 of x" (notice we replaced the entire phrase "the cost in 2000" with x). The word "of" means we multiply, so we can write "Oil is 90 a barrel = 1.75x". We can leave out any words that don't really matter to the math part of the problem such as "oil is and "a barrel" if you feel comfortable doing so. Leave out any steps you feel comfortable with, as what I am showing you is the most detailed you can get. I am just trying to show you how to literally translate the language of English to the language of math, and we end up with:
90=1.75x
Swap it around so the x is on the left:
1.75x=90
Divide both sides by 1.75 to cancel out the 1.75 in front of the x, or:
1.75x/1.75=90.00/1.75 which leaves us x=90.00/1.75
Now we solve for x. Do the simple math of 90/1.75 and
x=51.4285 and round to the nearest hundredth (since this is how we represent dollars)
x=51.43
If your teacher requires you to, don't forget to write this as a dollar value, since that is what the problem was looking for ($51.43).
Hope this helps you. After doing this a while, you will just be able to look at the problem and know to divide 90 by 1.75, but when just starting, show your work so your teacher can show you where you made a mistake, if you make one (everybody does...trust me). I've gotten many more wrong than I have right:)
Good Luck!
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