Multiply this 15 mph by the conversion factor derived from 1.6 km = 1 mi:
15 mph 1.6 km
------------ * ---------- = 24 km/hr
1 1 mi
The cyclist's speed in km/hr is 24 km/hr.
In 3 hrs the cyclist can cover (24 km/hr)(3 hr) = 72 km.
Answer:
She is at least 51. She could be older.
Let t be time and r be rate, then if time varies inversely with the rate, the equation is

. If it takes 5 hours to drive a fixed distance at a rate of 80, we can sub those values in to solve for the constant of variation, k.

. Solve for k by multiplying 5 and 80 to get that k = 400. Now let's find a new time t when r is a rate of 70. We will use that k value to do this:

and find that it will take 20 hours to drive the distance at 70 mph when it takes 5 hours to drive the distance at 80 mph. Makes sense that it takes longer to drive a fixed distance when you are going slower.
1. 13%
2. 53%
3. 47%
4. 6%
(all % decimals are rounded)
The answer to that is -4!!