Hello!
It's says it's 5 because 2.5 x 2= 5
2.5 plus 2.5 equals 5, because if you do 2.5 times 20 then it would be 50, just try to do it in your head, okay so, ask yourself whats 2.5+1= 3.5 okay but then add another 1 it would equal to 4.5 then add another .5 then it would equal to 5 see what I am getting at? (:
Hope this helps!.