of the 100 state parks 68 have fishing 46 have biking 4 have caving 2 have biking and caving 0 have fishing and caving 26 have biking and fishing how many parks allow these activities

it helps to draw three circles with each circle intersecting partially with the other two.

Each circle is labeled fishing, biking, or caving.

Because biking overlaps with caving (2) and fishing (36) and there is a total 46 biking, it leaves 8 potential for biking alone.

Because fishing overlaps with biking, it leaves 68-36 = 32 potential fishing alone.

And finally, there is a potential 2 camping alone because 2 of the 4 share biking.

Let's add up all the categories.

32 fishing

8 biking

2 caving

2 biking and caving

36 biking and fishing

Total = 80

But there are 100 state parks so there must be 100 - 80 = 20 parks that allow all three activites.