Given two 2s, "plus" can be changed to "times" without changing the results: 2 + 2= 2 x 2.
The solution with three numbers is easy too: 1 + 2 + 3= 1 x 2 x 3.
Now find the answer for 4 numbers and for 5 numbers.
The word One has 3 letters, in the word three there are 5 letters, in the word five there are four letters and four has four letters in it as well. Whatever number you'll go back to four, and that's why it's the magic number.