The number of vanilla cone she christina's sold after 20 day is 138.
Christina's ice cream parlor sold 60 vanilla cones on the first day of summer.
If the goal is to increase the number of vanilla cones sold each day by 4
Arithmetic progression is the series of number that have common difference between adjacent numbers.
Christina sold 60 vanilla cone at her first day. a=60
now each day is sells increase by 4 cones
so we common difference D = 4
The progression can be given as
S = a + (n-1)D
for 20th day = 60+(20-1)4
= 138
Thus the required number of vanilla cone she christina's sold after 20 day is 138.
Learn more about arithmetic progression here:
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