sameeruce08 wrote:

If bob house is halway between alice and destination and if slice speed is twice that of bob

How are they supposed to cross each other they will meet directly at destination

alice has to cover 2d distance with 12km/hr implies time taken is 2d/12=d/6

bob jas to travel d with speed 6km/hr hence time taken is d/6

so they meeet directly in destination

please explain

sameeruce08 , the "halfway" info is to let us know that Alice starts behind Bob.

As far as distance:

A does travel 2d, but we don't care about that because we don't know start times.

After she passes him, both travel same distance.

We find distance from her rate and time. In minutes. (Or fraction of hour.)

Then find Bob's time from distance and rate.

All that matters: separate rates and times.

She travels at 12 km per hour.

One hour = 60 minutes.

Rate: She travels 12 km in 60 minutes:

D= \((\frac{12km}{60mins}*10 minutes) = 2\)kms

Bob's speed = 6 km/hr, OR 6 km in 60 minutes.

Bob's time?

\(T = \frac{D}{R}\)

\(T=\frac{2}{(\frac{6}{60})}=(2*\frac{60}{6})=20\) mins

OR get time from Bob's unit rate = \(\frac{6km}{60mins} =\frac{1km}{10mins}\)

To go 2 km, at a rate of 1 km per 10 minutes, it will take him 2 * 10 = 20 minutes.

Hope that helps.

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