Question

A jet flew from Tokyo to Bangkok, a distance of $200$ km. On the return trip the speed was decreased by $50$ km/h. If the difference in the times of the flights was $2$ hour. What was the speed from Bangkok to Tokyo?

• A. $100$ km/h
• B. $50$ km/h
• C. $300$ km/h
• D. $400$ km/h

Answer 1

Answer: (B)

$50$ km/h

Time $=$ $\frac{distance}{speed}$
Let the going time, $t=\frac{200}{x}$
Return time: $t+2=\frac{200}{x-50}$
$\frac{200}{x}$ $+2=$ $\frac{200}{x-50}$
$200x-10000+2x^2-100x=200x$
On factoring we get,
$(x+50)(x-100)=0$
$x=100km/hr$ (neglecting the negative value of $x$)
so, speed from Bangkok to Tokyo is $(100-50)km/hr=50km/hr$