Math
posted by Jerald .
Mark and Sandy are participating in a BikeaThon for charity. Mark oversleeps, so Sandy gets a one hour head start and bikes at a speed of 12 miles per hour. To catch up to Sandy, Mark decides that he needs to bike at a speed of 15 miles per hour.
1. Make a chart that shows how far Mark and SAndy ride their bikes during the first three hours of the Bike a thon
Hour 1: Mark 15mph Sandy 12mph
Hour 2: Mark 30mph Sandy 24mph
Hour 3: Mark 45mph Sandy 36mph

You missed the fact that Sandy had a one hour head start.
At the end of:
Hour 1: Sandy  12 m; Mark 0
Hour 2: Sandy  24 m; Mark 15
Hour 3: Sandy  26 m; Mark 30 
Thank you.
2. WRite an expression that represents Sandy's journey. Be sure to define your variables
t=hour
12t + 12 
You're welcome.
12t 
But didn't she have a one hour head start so she would have had an extra 12 m?

You just need an expression that represents her journey. It doesn't make any difference what time she started.