A man ran 5 or 7 miles each day for 30 consecutive days. His total mileage during this period was 166.
How many days did he run 5 miles? And how many days did he run 7 miles?
F+S=30
5F+7S=166
multiply the top equation by five, and subtract the top from the bottom.
2S=150
S=16 days
F=14 days.