For sake of convenience, reverse the series, then it would be:
21,19,17.....7
a=21, d = -2,
s(4) = 4/2 (21+15)
s(4)=2(36)
s(4) = 72
Answer:
75 students
Step-by-step explanation:
500 students x 0.25 (25%) = 125 play baseball
500 students x 0.10 (10%) = 50 play soccer
125 who play baseball - 50 who play soccer = 75 more students who play baseball