Question

find the 21st term of the arithmetic sequence: 18,23,28,33,...

Answer 1

$18,23,28,33,... \\ a_1=18 \\ d=5 \\ \\ a_n=a_1+d(n-1) \\ a_{21}=a_1+20d \\ a_{21}=18+20 \times 5 \\ a_{21}=18+100 \\ \boxed{a_{21}=118}$