The speeds of three cars are in the ratio 5 : 4 : 6. The ratio between the time taken by them to travel the same distance is 

The speed and time are inversely proportional to each other when the distance is constant

SInce the ratios of the speeds are $5:4:6$, the ratios between the time taken by them is $\frac{1}{5}:\frac{1}{4}:\frac{1}{6}$

Multiply all ratios with 60

Hence, the ratios are $12:15:10$