The probability of the spinner stopping on a 1, 2, 3 or 4, would be 100%, since these are the only numbers on the spinner (it is always going to land one of these numbers).
The probability of landing on 1, would be 25%, because there are 4 sections, each with a different number on it. So 100% divided by 4, is 25%.
Now, for your question. What is the probability that it would land on 1, 2 or 3? The answer would be 75%, because now we are no longer dealing with one section of the spinner, but rather three sections, so we can multiply 25% by 3, and that gives us 75%.
Short answer:
75% because the sections 1, 2 and 3 take up 75% of the spinner.