Math Problem Statement

A driver made a trip consisting of two parts. During the first part, he travelled 200 miles and the second part 225 miles. The second part of the trip took him an hour longer than the first part. If the rate at which he was travelling during the first part was 10 miles per hour faster than the rate during the second part, what was the total time of the trip.

Solution

Let's define the variables for the rates and times of the two parts of the trip:

  • Let r1r_1 be the rate during the first part of the trip (in miles per hour).
  • Let r2r_2 be the rate during the second part of the trip (in miles per hour).
  • Let t1t_1 be the time for the first part of the trip (in hours).
  • Let t2t_2 be the time for the second part of the trip (in hours).

We know the following information:

  1. The distance for the first part of the trip is 200 miles, and for the second part, it is 225 miles.
  2. The time for the second part, t2t_2, is 1 hour longer than the time for the first part, t1t_1. Hence, t2=t1+1t_2 = t_1 + 1.
  3. The rate during the first part, r1r_1, is 10 miles per hour faster than the rate during the second part, r1=r2+10r_1 = r_2 + 10.

Now, let's use the formula Distance=Rate×Time\text{Distance} = \text{Rate} \times \text{Time} for both parts of the trip:

For the first part: t1=200r1t_1 = \frac{200}{r_1} For the second part: t2=225r2t_2 = \frac{225}{r_2}

From the information t2=t1+1t_2 = t_1 + 1, we can substitute the expressions for t1t_1 and t2t_2:

225r2=200r1+1\frac{225}{r_2} = \frac{200}{r_1} + 1

Also, from r1=r2+10r_1 = r_2 + 10, we can substitute r1r_1 in the equation:

225r2=200r2+10+1\frac{225}{r_2} = \frac{200}{r_2 + 10} + 1

Now let's solve this equation. First, multiply both sides by r2(r2+10)r_2(r_2 + 10) to clear the denominators:

225(r2+10)=200r2+r2(r2+10)225(r_2 + 10) = 200r_2 + r_2(r_2 + 10)

Expand both sides:

225r2+2250=200r2+r22+10r2225r_2 + 2250 = 200r_2 + r_2^2 + 10r_2

Simplify the equation:

225r2+2250=200r2+r22+10r2225r_2 + 2250 = 200r_2 + r_2^2 + 10r_2

225r2+2250=210r2+r22225r_2 + 2250 = 210r_2 + r_2^2

Now, move all terms to one side:

225r2210r2+2250=r22225r_2 - 210r_2 + 2250 = r_2^2

15r2+2250=r2215r_2 + 2250 = r_2^2

Rearrange the equation into standard quadratic form:

r2215r22250=0r_2^2 - 15r_2 - 2250 = 0

Now, solve the quadratic equation using the quadratic formula. The quadratic formula is given by:

r2=b±b24ac2ar_2 = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}

For the equation r2215r22250=0r_2^2 - 15r_2 - 2250 = 0, a=1a = 1, b=15b = -15, and c=2250c = -2250. Substituting these values into the quadratic formula:

r2=(15)±(15)24(1)(2250)2(1)r_2 = \frac{-(-15) \pm \sqrt{(-15)^2 - 4(1)(-2250)}}{2(1)}

r2=15±225+90002r_2 = \frac{15 \pm \sqrt{225 + 9000}}{2}

r2=15±92252r_2 = \frac{15 \pm \sqrt{9225}}{2}

r2=15±962r_2 = \frac{15 \pm 96}{2}

So, the two possible solutions are:

r2=15+962=1112=55.5orr2=15962=812=40.5r_2 = \frac{15 + 96}{2} = \frac{111}{2} = 55.5 \quad \text{or} \quad r_2 = \frac{15 - 96}{2} = \frac{-81}{2} = -40.5

Since speed cannot be negative, we take r2=55.5r_2 = 55.5 miles per hour.

Now, since r1=r2+10r_1 = r_2 + 10, we have:

r1=55.5+10=65.5miles per hourr_1 = 55.5 + 10 = 65.5 \quad \text{miles per hour}

Calculating the Total Time:

Now that we know the rates, we can calculate the times for each part of the trip.

For the first part: t1=20065.53.05 hourst_1 = \frac{200}{65.5} \approx 3.05 \text{ hours}

For the second part: t2=22555.54.05 hourst_2 = \frac{225}{55.5} \approx 4.05 \text{ hours}

Thus, the total time of the trip is:

t1+t23.05+4.05=7.1 hourst_1 + t_2 \approx 3.05 + 4.05 = 7.1 \text{ hours}

Final Answer:

The total time for the trip is approximately 7.1 hours.


Would you like further explanation or a breakdown of any steps? Here are some related questions you might find helpful:

  1. How can you verify the solution to this problem?
  2. What happens if the rates for both parts are equal?
  3. How can the relationship between time and speed be used to solve similar problems?
  4. How do you apply the quadratic formula in real-world scenarios?
  5. What would happen if the second part took two hours longer than the first?

Tip: Always check for the reasonableness of your solutions, especially when dealing with physical quantities like speed and time!

Ask a new question for Free

By Image

Drop file here or Click Here to upload

Math Problem Analysis

Mathematical Concepts

Algebra
Quadratic Equations
Rates and Proportions

Formulas

Distance = Rate × Time
Quadratic Formula: x = (-b ± √(b² - 4ac)) / 2a

Theorems

Quadratic Formula

Suitable Grade Level

Grades 9-12