In half an hour the trains travels 22.5 miles
<h2>
Hello!</h2>
The answer is: 23.77 hours
<h2>
Why?</h2>

Where:
Total(t) is equal to the amount for a determined time (in hours)
<em>Start</em> is the original amount
<em>t </em>is the time in hours.
For example, it's known from the statement that the bacteria double their population every 15 hours, so it can be written like this:

To calculate how long it takes for the bacteria cells to increase to 300, we should do the following calculation:

So, to know if we are right, let's replace 23.77 h in the equation:
Total(t)=100*2^\frac{23.77}{15}=299.94
and 299.94≅300
Have a nice day!
Answer:
and not 
Step-by-step explanation:
Jim's work evaluating
is shown:

If you look at the Second step, the exponent is taken over only the numerator. It should have been taken over both the numerator and denominator as shown below.

The correct workings therefore is:

The easiest way, I think, is to convert the mixed number into an improper fraction, then multiply by 3.
3 1/2 = 7/2
7/2 · 3 = 21/2
now just change the improper fraction back to a mixed number by dividing and putting the remainder into fraction form
21/2 = 10 1/2
You could also multiply the whole number by 3 and the fraction by 3, ending up with 9 3/2, but then have to convert the improper fraction into a mixed number
3/2 = 1 1/2
then add the numbers together
9 + 1 1/2 = 10 1/2
either way works, whatever is easiest for you.
A)
if 39.99 is the 100%, what is 10 in percentage? well

solve for "x".
b)
now, with the discount, the amount is 29.99, thus if 29.99 is the 100%, what is 1.95 from it in percentage?

solve for "x".
c)
the original price is 39.99, the markup on that is 60%, how much is that?
well

now, after the discount, the price is 29.99, how much is 23.994 in percentage of 29.99?
well

solve for "x".