Traveling at a constant rate of 15 miles per hour, it took Bob x hours

Question

Traveling at a constant rate of 15 miles per hour, it took Bob x hours to go from his home to his school. Traveling at a constant rate of 20 miles per hour, it took Bob x − 1 hours to travel the same route. What is the value of x?

A 2
B 3
C 4
D 5
E 6

A 2
B 3
C 4
D 5
E 6

KSBGC · Answer

15x = 20(x-1)

15x = 20x -20

x = 4.

*** Distance = time * speed.

EgmatQuantExpert · Answer

Solution 
  Given:  
 •  s_1 = 15  miles per hour, and  t_1 = x  hours
•  s_2 = 20  miles per hour, and  t_2 = x – 1  hours
• Both distances are same

To find:  
 • The value of x

Approach and Working:   
We know that distance = speed * time
 • Implies,  s_1 * t_1 = s_2 * t_2 
• Thus, 15x = 20(x - 1)

Therefore,  x = \frac{20}{5} = 4

Hence, the correct answer is Option C

Answer: C

https://e-gmat.com/blogs/wp-content/uploads/2018/08/Ability-Quiz-WP-e1533292133520.png

KarishmaB · Answer

Using logic, we know that in second case, Bob travelled 1 hr less because he travelled 5 miles extra for each of the (x - 1) hrs. This is the distance he would have covered in the last hour in the first case.

5*(x - 1) = 15
x = 4

Answer (C)

Abhishek009 · Answer

Let the distance travelled be 60 miles (LCM of 15 & 20)

So, Travelling at 15 miles/hour time taken is 4 hours & Travelling at 20 miles/hour time taken is 3 hours

Thus, the value of x is 4, Answer must be (C) 4

philipssonicare · Answer

When I first saw these types of questions I could answer the simple ones, but was still confused by the units. I'm putting the below for others in similar situations.

1st trip  \frac{15(miles)}{1(hour)}·x(hours)=distance

2nd trip  \frac{20(miles)}{1(hour)}·(x-1)(hours)=distance

The distance is the same in both so we can have the equations equal each other

\frac{15(miles)}{1(hour)}·x(hours)=\frac{20(miles)}{1(hour)}·(x-1)(hours)

Simplification: Each side has  hours  in the denominator and numerator so they can be cancelled from each side. Just remember that we're trying to find  x  and it uses the unit  hours

\frac{15(miles)}{1}·x=\frac{20(miles)}{1}·(x-1)

Simplification: Both sides of the equation use the unit  miles , so it can be cancelled from both sides of the equation.

\frac{15}{1}·x=\frac{20}{1}·(x-1)

15x=20x-20
0=5x-20
0=x-4
4=x

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Traveling at a constant rate of 15 miles per hour, it took Bob x hours

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Traveling at a constant rate of 15 miles per hour, it took Bob x hours

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