Question 54
A triangular number is the number of circles you can place in an equilateral triangle of a certain height. For example, in the figure on the right, you can see that the fourth triangular number is $10$. Jasmine writes down the first $1000$ triangular numbers: $1$, $3$, $6$, $10$, $15$, $\ldots$.
How many of these numbers end in a $0$?
How many of these numbers end in a $0$?