The experimental probability is the probability that’s we obtain from an experiment (from trials) here rolling the die and noting the number. Luka rolled ten times and 5 of these yielded a number less than 5 (the numbers on a 6-sided die that are less than five are 1, 2, 3, 4). So there were 5 out of 10 times that a number rolled was less than 5. This makes the experimental probability 5/10.
The theoretical probability is obtained through mathematical thinking (not by trying it an keeping track). On a 6-sided die there are 4 numbers less than 5. There are 6 numbers in all. Every number is equally likely to appear so the probability that a number rolled is less than 5 is 4/6. This is the theoretical probability.
As an aside, the more times you roll (100, 1000, 1000000 rolls) the closer the experimental probability (what you observe) gets to the theoretical probability (what you would expect by reasoning it out mathematically).
