Question

5. The time needed to travel from one place to another is inversely proportional to the speed. A person
travelling 72 km/hr can go from Dehradun to Lucknow in 10 hours. How fast must the person travel to
make the trip in 9 hours? answer is 80 km/h​

Answer 1

Answer:

80 km/h

Step-by-step explanation:

Let speed be 'x'Km/h when person takes 9 hours

Now, 72*10 = x*9

==> 720÷9 = x

==> 80 = x

Speed = x Km/h

= 80 Km/h

Answer 2

Speed would be 80 km/h

Step-by-step explanation:

Consider t represents time and s represents the speed,

∵ The time needed to travel from one place to another is inversely proportional to the speed,

That is, $t\propto \frac{1}{s}$

$t=\frac{k}{s}$,                     ...............(1)

Where,

k = constant of proportionality,

if s = 72 km/hr, t = 10 hours,

$10=\frac{k}{72}$

$\implies k = 720$

From equation (1),

$t=\frac{720}{s}$,

if t = 9 hours,

$9=\frac{720}{s}$

$\implies s =\frac{720}{9}=80\text{ km per hour}$

Hence, speed would be 80 km/h

#Learn more :

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