convertions 80km/hr - meters/second

cgc wrote:It is not terribly difficult but I find myself taking too long to answer this question. How would you approach this question to answer it fast?

How many seconds will it take for a bus that is traveling at a constant rate of 80 kilometers per hour to travel a distance of 400 meters? (1km = 1000 meters)

(a) 5
(b) 12
(c) 18
(d) 20
(e) 30

Cheers,

Here's an approach you can pretty much do in your head.
First recognize that 80 km = 80,000 m, so the bus travels 80,000 meters per hour.
We can see a relationship between 80,000 and 400
In your head, you might begin by seeing that, in 1/2 an hour, the bus would travel 40,000m (we now have the "4" part, but we want 400m not 40,000m)
From here we can see that, in 1/20 of an hour, the bus would travel 4,000m (closer)
So, in 1/200 of an hour, the bus would travel 400m --> great, the answer is 1/200 of an hour (almost done).

Convert 1/200 hours to seconds.
Since 1 hour = 3600 seconds, we want 1/200 of 3600, which equals 18.