Explanation

The given series is: 1, 1, 2, 3, 5, ___?

This follows the Fibonacci sequence, where each number is the sum of the previous two numbers:

• 1 + 1 = 2
• 1 + 2 = 3
• 2 + 3 = 5
• 3 + 5 = 8

Thus, the missing number is 8.