Penny a Day

You have just won a contest!
You must choose between 2 prizes. You may choose $.75 a day for 15 days or you may choose a penny the 1st day, which doubles every day for 15 days. Find out which prize you would choose.
Please do a writing (using good math language and symbols), which tells how and why you made your choice. Include a chart, graph or table that helped you solve the problem.

Farmer Fiona

Farmer Fiona raises cows and chickens. In all, her animals have 20 heads and 70 legs. How many cows and chickens does she have?  Please remember to fully explain your thinking and the strategy you used.