Terri can swim 3 laps in 2.5 minutes. To find how long it takes to swim 20 laps, you can make a proportion.
[tex] \frac{Lap}{Time} [/tex]
Put the amount of laps on the top and the time(minutes) at the bottom.
[tex] \frac{3}{2.5} = \frac{20}{x} [/tex]
Cross multiply:
[tex] 20 \times 2.5 = 50 [/tex]
Divide by 3:
[tex] 50 \div 3 = 16 \frac{2}{3} \rightarrow 16.67 [/tex]
It would take Terri [tex] 16 \frac{2}{3} [/tex] OR [tex] 16.67 [/tex] minutes to run 20 laps.
