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I am having difficulty with this problem , am I doing something wrong here ?

To mail an airmail a letter costs $60$ cents for the first half ounce and $15$ cents for each additional ounce or fraction thereof.What would be the cost of mailing a letter that weighs $2.1$ ounces.

Here is how I am doing it:

$$\frac{2.1}{0.5}=4.2 \text{ parts}.$$

Since the First part costs $60$ cents so $4.2-1 = 3.2$. This means

$$1 + 3.2 = 60 \text{ cents} + 3.2(15 \text{ cents}) = 60 \text{ cents} + 48 \text{ cents} = 1.08 \text{ dollars}.$$

However the answer is supposed to be $1.20$. Any suggestions on what I am doing wrong?

  • 1
    The answer is wrong as well. You pay 60 cents for the first half ounce; then you pay 15 more cents for one more ounce, which means 75 cents will pay for a letter between 0.5 and 1.5 ounces; another 15 cents will pay for a letter between 1.5 and 2.5 ounces, so you only need to pay 90 cents.2012-07-13

2 Answers 2