If you think of the "for every" as a : then it will make sense. So, replace the "for every" with a :. So: There are 5 strawberries for every 6 apples Turns into strawberries:apples = 5:6
For every means for example if there is going to be one apple there will always have to be 2 orananges so every time one apple adds there will be always 2 oranges