Find the last two digits of the following sum: 5 + 10 + 15 + \cdots + 100.
We know that \(100 + 5 = 105\)
We also know that \(50+55 = 105\)
There are 10 cases of this, so the sum is \(10 \times 105 = 1050\)
Can you find the last 2 digits from here?