4 digit numbers For divisibility by 55 , no. should be div. by 5 and 11 both Also, for divisibility by 11
a+c=b+5 for b=1‌‌a=2,‌‌c=4 a=4,‌‌c=2 for b=2‌‌a=3,‌‌c=4 a=4,‌‌c=3 for b=3‌‌a=6,‌‌c=2 a=2,‌‌c=6 ∴6 possible four digit no.s are div. by 55 (II) 5 digit number is not possible