Ryan added 10 fish to his pond each day for 80 days. What was the total change in the number of fish in the pond?
Solution:
10 fish to his pond each day for 80 days.
The total change in the number of fish in the pond =
a = first term = 10
d = common difference = 10
number of terms = 10
Sn = n/2 ( a + ( n- 1 ) d)
S80 = 80/2 ( 10 + ( 80 - 1 ) 10 )
= 40 ( 10 + 79 x 10)
= 40 ( 10 + 790)
= 40 ( 800)
= 32,000 fishes
