How long will it take to travel 15kms in a car going 90km per hour?

Question

I know the answer is 10 minutes but not sure how the equation works.

I'd like to be able to do these questions in under 1 minute without a calculator.

I know it has something to do with the rate in hours and the answer in mintues but I cant figure it out.

Answer 1

Distance equals Rate multiplied by Time, or d = r x t. Since we're solving for time, we write t= d/r. The distance equals 15km and the rate is 90 km/h. (15 km)/(90 km/h) = (1/6)h or "one-sixth of an hour." Convert this to minutes.

 

(1 h)/6 * (60 min/h) = 10 min.

 

Thus, the answer is 10 minutes.

Answer 2

The formula for rate is one quantity/time 

so 90/1=90

90*15=1350