Tiara earned 10 dollars on her first day selling lemonade, and she was determined to earn 3 more dollars each day than she had made the day before. If she met this goal exactly, how much money did she earn, in total, for her first 20 days selling lemonade? A. $770 B.$520 C.$67 D. $70
In this problem we have an arithmetic sequence
the first term is
a1=10
a2=10+3=13
a3=13+3=16
The common difference is d=3
The general expression is equal to
an=a1+d(n-1)
substitute the given values
an=10+3(n-1)
so
For n=20 days
substitute
a_20=10+3(20-1)
a_20=10+3(19)
a_20=$67
therefore
the answer is the option C