Word Problem - Adding an amount after a certain limit I cant solve this word problem:


Courier charges to a certain destination are $65$ cents for first $250$ grams and $10$ cents for each additional $100$ grams or part thereof. What could be the weight of package for which charge is  $\$ 1.55$  ?


I am solving it as:
$155 $cents = $65 + 90$ = $250$ grams + $900$ grams (since $10$ cents is for $100$ grams)
I get the answer $1150$ but the answer is suppose to be $1145$.
 A: Suppose you have a package that weights 100 grams. How much does it cost to ship? How about for 200 grams? 300? 400?
Can you describe in words how you calculate the cost if you know the weight. Now let $W$ stand for the weight of the package and $C$ for the cost to ship it. Then turn your description into a mathematical equation.
A: We use your analysis. We paid an extra $90$ cents.  For that, we could ship a package that weighs $250+ \frac{90}{10}(100)$ grams, that is, $1150$ grams.
But note that the fine print says that we pay $10$ cents for every $100$ grams or part thereof. So if we are "over" the basic $250$ grams, say by $802$ grams, we pay $80$ cents for the $800$ grams, and an extra $10$ cents for the measly $2$ extra grams over $800$. In effect, we are paying as if our package weighed $250+900$. (So we might as well open the package and put a couple of cookies in. The shipping cost won't change.)
Mathematically, all one can say is that if we paid $\$1.55$ to ship the package, then the weight $w$ of the package satisifes the inequality
$250+800 \lt w \le 250+900$, that is,
$$1050 \lt w \le 1150.$$
If the question was a multiple choice question, and $1145$ was the only "answer" supplied that is in the above interval, then $1145$ is the right answer. 
