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the tcs office at siruseri is at a distance of 21km from baburaj’s home.when he leaves home 10 minutes late his travel time increases by 40% if leaving late decreases his average speed by 12kmph how long does his commute take when he leaves on time
a)1 hour b)21minutes c)30 minutes d)40 minutes
Asked in/Preparing for : tcs


1 Respond



Total Distance `= 21` Km.

Let original time `= t`

Average Speed `= 21/t`

On leaving late `10` min `(1/6)` h, his travel time increase by `40%` .

This travel time `= t + 40% ` of `t` `=> 1.4t` .

His average Speed when he leaves `10` minutes late `= 21/(1.4t) ` -------------- (1)

His Average speed decrease by `12` kmph.

Now his average speed `= 21/t - 12` ----------------------- (2)

On equating equation (1) and (2),

`21/(1.4t) = 21/t - 12`

`=>` `21/(1.4t) = (21 -12t)/t`

`=>` `21t = 29.4t - 16.8t^2`

`=>` `16.8t^2 - 8.4t = 0`

`=>` `8.4t (2t -1) = 0`

Either,
`8.4t = 0`
`=>` `t = 0` (not possible.)

Or,
`2t -1 = 0`
`=>` `t = 1/2` h
`=>` `t = 30` minutes.
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