Question 20
The $2019$ lockers of the $2019$ students of a school are numbered with the squares of the first $2019$ positive integers, that is, the first locker has number $1^{2}=1$, the second locker has number $2^{2}=4$, the third locker has number $3^{2}=9$, and so on up to the last locker, which has number $2019^{2}=4076361$.
a) How many digits were used to paint the first hundred lockers?
b) Adding all the locker numbers, what is the units digit of this result?
a) How many digits were used to paint the first hundred lockers?
b) Adding all the locker numbers, what is the units digit of this result?