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At the start of the new year, the price for a gallon of milk at a local grocery store increased by 2.4% as a result of inflation. If a gallon of milk cost $2.92 last year, about how much does it cost this year?

A.  $2.84 
B.  $2.99  
C.  $3.62  
D.  $5.32  
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3  
What have you tried? –  Cameron Buie May 22 '13 at 22:17
    
Since you are new, I want to give some advice about the site: To get the best possible answers, you should explain what your thoughts on the problem are so far. That way, people won't tell you things you already know, and they can write answers at an appropriate level; also, people tend to be more willing to help you if you show that you've tried the problem yourself. If this is homework, please add the [homework] tag; people will still help, so don't worry. –  Zev Chonoles May 22 '13 at 22:22
    
adding i think it is a –  bob hhhhhhhhh May 22 '13 at 22:22
    
This type of problem is better addressed at algebra.com where you can submit trivial questions and others are willing to offer a tutor-level answer. –  JoeTaxpayer May 22 '13 at 22:35

3 Answers 3

Hint: If I have a number $z$, and I

increase $z$ by $p$ percent

that means

take $z$, and then add to it $p$ percent of $z$

Remember, the quantity "$p$ percent of $z$" is defined to be the expression $$\frac{p}{100}\times z,$$ so that for example, $15$ percent of $200$ is $$\frac{15}{100}\times 250=37.5.$$

Now, let $x$ be the amount that milk cost last year.

Write down the expression for $2.4$ percent of $x$:

$$\fbox{$\strut\quad\qquad^\strut_{\strut}$}$$

and add that to $x$:

$$x+\;\fbox{$\strut\quad\qquad^\strut_{\strut}$}$$

We are told that this quantity is equal to the price of milk this year: $\$2.92$. Now solve for $x$.

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So the price of my favorite bike was $\$100$ last year. They increased the price by $\%5$ this year. What would be the new price?

It was $\$100$ last year. What is $\%5$ of $\$100$? Note that $\%5$ is equivalent to saying $\frac{5}{100}$, so $\%5$ of $\$100$ is $\frac{5}{100} \times \$100 = \$5$. Hence, the new price is $\$100+\$5 = \$105$.

Now, you do the same thing for your question, and let me know if you have any problems.

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This is the solution $(2,4/100)*2,92 +2,92=2,99$!

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