Question

21 +22+23+.....+60 find the sum

Answer 1

Answer:

First term: let it be a=21

Common difference =1

Last term=an=60

Sn =n/2 ( a+an)

an= 60= a+(n-1)d

60= 21+(n-1)(1)

60-21/1=n-1

39=n-1

40=n

Sn= 40/2(21+60)

Sn= 20×81

= 1620