Mr S drives to a meeting 30km from meeting place he realise he is going to be 15 min late,if he continues the highest aloud speed 80km/h .
How many minutes would he be late if he would drive 70km/h ? And at what speed should he be driving to make it in time?

I assume he realizes this just as he starts the trip.

Let $T$ be the time allowed to make the 30km trip if he is to be on time.

$30 = 80(T+0.25)$

$T = \dfrac 1 8~hr$

At 70 km/hr

$t = \dfrac{30}{70} = \dfrac 3 7 ~hr$

$\dfrac 3 7 - \dfrac 1 8 = \dfrac{24 - 7}{56} = \dfrac{17}{56}~hr$

So he would be $\dfrac{17}{56}~hr \approx 18.2~min$ later if he drives at 70 km/hr

I leave the last one for you. You know how long he's got to make the trip, $\dfrac 1 8~hr$, and you know the distance. You can divide I'm sure.

Thank you! I tried to make hours into seconds.

Could you please explain where you got 0.25 from?

Originally Posted by ceedee
Could you please explain where you got 0.25 from?
really?

$\dfrac{15}{60} = 0.25$

$\dfrac{15}{60} = 0.25$