Two people walk the same distance of 15 miles, in which A spends 15 mi

Question

Two people walk the same distance of 15 miles, in which A spends 15 minutes less than B, and the speed of B is 10 miles/h slower than the speed of A. What is the speed of B?

A. 12 miles/h 
B. 15 miles/h 
C. 18 miles/h 
D. 20 miles/h 
E. 21 miles/h

Tejas10 · Answer

I solved this question by putting values;

D=15mph for both

Let time for B be 30 mins and that for A be 15 mins.

So, Speed of A will be 15x60/15 = 60m/hr and speed of B will be 15x60/30 = 30mph
Difference between speeds is 60-30=30 - not satisfying the question

Let Ta=30. So Sa=15×60/30= 30mph
Let Tb=45. So Sb=15×60/45= 20mph
Difference in speeds = 10mph - SATISFYING THE QUESTION

Hence, D

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Bunuel · Answer

This question is a part of  Are You Up For the Challenge: 700 Level Questions  collection.

ShahadatHJ · Answer

Distance 15 Miles
Speed A = X
Speed B = X-10
ATQ, 
 \frac{15}{X} + \frac{15}{60} = \frac{15}{X-10}
 
---
---
---
 X^2 + 10X  =  600 
 X^2 + 10X-600  =  0 
---
---
---
X = 30 or -20
B's Speed 30-10 = 20 MPH
Ans. D

danbrown9445 · Answer

Algebraic way
Speed of A = y
Speed of B = y-10
Time taken by A to travel 15 miles =  \frac{(x-15)}{60}  hours
Time taken by B to travel 15 miles =  \frac{x}{60}  hours

Distance travelled by both are same
 y*\frac{(x-15)}{60} = (y-10)\frac{x}{60}

y(x-15)=x(y-10)

x=\frac{3y}{2}

Distance = speed*time
 15 = (y-10)*\frac{x}{60}

15 = (y-10)*\frac{3y}{2*60}

y^2-10y-600=0

Test answers to get y = 20

PSKhore · Answer

Can someone let me know why can't we use the equation (3/4)ts = t(s-10)
s=40
therefore speed of B is 30 mph???

GraemeGmatPanda · Answer

I'm not sure where your 3/4 comes from but if it's coming from the '15mins less' that's effectively assuming that the time for B to walk the distance is 1h (which we don't know and is incorrect!)

Hope this helps

Two people walk the same distance of 15 miles, in which A spends 15 mi

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Two people walk the same distance of 15 miles, in which A spends 15 mi

Prep Toolkit

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