Question

Bolt is preparing himself to participate in a marathon by running daily 21 miles. One fine day, after running 10 miles, he takes a break and resumes running at the rate of 9 miles per hour for $n$ minutes. Which of the following equation best models the situation?

• A. $10+9n=21$
• B. $10=21+9n$
• C. $10+9\left(\frac{n}{60}\right)=21$
• D. $10=21+9\left(\frac{n}{60}\right)$

Answer 1

The correct option is C $10+9\left(\frac{n}{60}\right)=21$

Let's look at the options first.
Since we know that Bolt runs 21 miles every day, therefore, option B & option D cannot be the correct answer.

Now we are left with the options A & option C.

Lets read the second statement in the question.
“ Running at the rate of 9 miles per hour for $n$ minutes “.
Since the rate is given in miles per hour but $n$ is given in minutes, therefore we have to convert $n$ minutes into hour by dividing by 60.
$\Rightarrow$$\left(\frac{n}{60}\right)hr$

Now, when we look at the options A & C, we can clearly mark option C as the answer.