Question

P and q walk around a circular track. they start at 6a.m. from the same point in the opposite directions. both walk at a speed of 3 rounds per hour and 4 rounds per hour respectively. how many times shall they cross each other before 8a.m. ?

Answer 1

Let the diameter of the circular path be D

The circumference of the path = πD

Speed of P = 3πD/h

Speed of P = 4πD/h

Since they are moving in opposite directions and moving along the circular path, it will be like they are approaching on another;

Their combined speed (approach speed) = (3πD + 4πD)/h

                                                                  = 7πD/h

Time taken for them to meet = Distance(Circumference)/Combined speed

                                              = πD/7πD

                                              = 1/7 hours

From 6.00 am to 8.00 am is 2 hours

Therefore, the number of times they will cross each other = 2 / (1/7)

                                                                                            = 14 times

Answer 2

Answer:

Answer

Correct option is

C

7

Relative speed = (2 + 3) km/hr = 5 km/hr This means that A and B cross each other 5 times in a hour and at least 2 times in half an hour

∴ They cross each other 7 times before 9:30 a.m.

Step-by-step explanation:

Explanation:

Relative speed = Speed of A + Speed of B (because they walk in opposite directions)

=

2

+

3

=

5

rounds per hour

Therefore, they cross each other

5

times in

1

hour and

2

times in

1

2

hour

Time duration from

8

a.m. to

9.30

a.m.

=

1.5

hour

Hence they cross each other

7

times before

9.30

a.m.