in this question, when i convert the speed from second to minute and then applying the D=ST formula

the answer is different and this answer is wrong.

where as,

when i’m applying the D=ST formula in starting and then converting it into minutes then answer is different.

Can anybody tell me, if gre like do everything and then convert the final answer into desired one or vice versa ?

can you show your rough work? Really hard to tell where you’re making mistake as the workflow is quite straightforward

Because D=(S \times T) \text{ or } T=\dfrac{D}{S}

And we’re given speed in km/s and question ask in km/min.

\dfrac{14 \times 10^8}{3 \times 10^5}= \dfrac{14 \times 10^3}{3} km/s

1min = 60sec or \frac{1}{60}min=1sec

Hence, \dfrac{14 \times 10^3}{3} km/s will be

\dfrac{\frac{14 \times 10^3}{3}}{60} \text{ or }\dfrac{14 \times 10^3}{3} \times \dfrac{1}{60} km/min

Using Calculator

we get 77.77 and as question said "**approximately** ", the closest option is A

Now if you want, you can directly convert 3 \times 10^5 km/sec to km/min by multiplying it by 60

You’re converting it wrong. You’re given 3\times10^5 km/sec

so, for 2 sec it will be : 2 \times(3\times10^5)

Thus, for 60sec or 1min it will be 60 \times (3\times10^5)

Thanks, got it.