Mulitples of 2 as well as of 5 between 1 and 500 are 10, 20, 30 …. 490
nth term an = last term (l) = 490
∴ Sum of n terms between 1 and 500,
Sn=n2[a+l] ...(i)
∵ an=a+(n−1)d=l
⇒10+(n−1)10=490
⇒(n−1)10=480
⇒n−1=48⇒n=49
From Eq. (i)... S49=492(10+490)
=492×500
=49×250=12250