Posted by Giovanna on .
a model airplane flies 18 feet in 2 seconds. What is the airplane's speed in miles per hour?

algebra 1 
Ms. Sue,
It travels 9 feet per second.
9 * 60 * 60 = 32,400 feet per hour
To find the miles per hour, divide:
32,400 / 5,280 = ? miles per hour 
algebra 1 
bobpursley,
long ago I memorized a conversion factor:
60mph=88fps
18/88=x/60 will do it. 
algebra 1 
bobpursley,
oops...
9/88=x/60 will do it. 
algebra 1 
Ms. Sue,
When I was a kid, my dad was appalled that I didn't know that 5,280 feet = 1 mile. Since we were on a long car trip, I had plenty of time to memorize that number. I still remember it after 60 years. <g>