Question

How many integers strictly between 0 and 10000 have exactly one digit equal to 5?

Answer 1

So that's an AP
a=5
d=10
tn= 995

tn= a+ (n-1)d
995= 5 + (n-1)10
995= 5 + 10n-10
995= -5+10n
1000=10n
n= 100