Question

a boy runs for 10 munites at a uniform speed of 9km/h at what speed should he run for the next 20munites so that the average speed becomes 12km/h

Answer 1

Hii...
Here is your answer..❤️

Solution:-
Speed of boy =9km/h
Time =10min
To convert it in hours we'll divide it by 60
$= > \frac{10}{60} hrs$
Since,
$speed = \frac{distance}{time}$
So,
$distance = speed \times time$
Distance=
$= > 9 \times \frac{10}{60} \\ = > 1.5km = \frac{15}{10} km$
Now,
Time taken 2nd time =20min
$= > \frac{20}{60} hrs$
Let the speed travelled be x.
So,
Distance=Speed×Time
$= > x \times \frac{20}{60} \\ = > \frac{20x}{60}$
Now,
$average \: speed = \frac{total \: distance}{total \: time}$
$= > 12 = \frac{( \frac{15}{10} + \frac{x}{3}) }{ \frac{(10 + 20)}{60} }$
$= > 12 = \frac{ \frac{15}{10} + \frac{x}{3} }{ \frac{1}{2} }$
$= > 12 \times \frac{1}{2} = \frac{15}{10} + \frac{x}{3}$
$= > 6 = \frac{15}{10} + \frac{x}{3}$
$= > \frac{x}{3} = 6 - \frac{15}{10}$
$= > \frac{x}{3} = \frac{60 - 15}{10}$
$= > \frac{x}{3} = \frac{45}{10}$
$= > x = \frac{45 \times 3}{10}$
$= > x = \frac{135}{10}$
$= > x = 13.5$

Hence,
Second speed is 13.5km/h

Hope it helps uh...✌️✌️✌️