Q. Prove that if n is any non negative integer whose decimal representation ends in 5, then 5 | n.
Solution
If n end in 5, then we can write as follows. then n=10m+5, for some whole number
m since 10 = 2*5 n can be written as n = 2*5m + 5 = 5(2m+1) = 5* something which is multiple
of 5 thus 5 divides n thus 5 | n Hence it is proved