Chloe drives from her house to her Grandma's house 48 miles away in an hour and 12 minutes. How fast was she driving on average?

4 mph

67 mph

90 mph

40 mph

To find a speed in miles per hour, we need to divide a number of miles by a number of hours.

We are given 48 miles, so we already have a number of miles.

We are given the time as 1 hour and 12 minutes. We need to convert this time into hours.

1 hour + 12 minutes = 1 hour + 12/60 hour = 1.2 hours

speed = distance/time = 48 miles / 1.2 hours = 40 mph

Answer: The fourth choice, 40 mph.

Working in minutes might give us a little more flexibility here, so we can start by converting 1 hour and 12 minutes, giving us 60 + 12 = 72 minutes for Chloe to drive 48 miles.

We can write her Chloe's rate then as 48 mi/72 min; since 48 and 72 have the factor 12 in common, we can reduce this to a rate of 4 mi/6 min. We want to find how many miles Chloe would travel in 60 minutes at that rate. Since 60 = 6 x 10, we can scale the rate up by a factor of 10, getting us a rate of 4 x 10 = 40 mi/60 min, or 40 mph.