Question

a) Find the sum of all three digit numbers which are divisible
by 11.​

Answer 1

110, 121, 132 .....................990

sn = n/2 (2a + (n-1) d )

therefore by solving from this formulae answer is

= 44550

Answer 2

Step-by-step explanation:

a=110

d=11

an=990

an=a+(n-1)d

990=110+11n-11

990+11-110=11n

891=11n

n=81

now sum

n/2[2a+(n-1)d]

81/2[220+880]

81/2[1100]

81×550

44550

Hope it may help you.