How many ways can 2 pens be chosen from 4 pens?

The number of ways to choose 2 pens from 4 pens can be calculated using the combination formula ( \binom{n}{r} ), where ( n ) is the total number of items and ( r ) is the number of items to choose. Here, ( n = 4 ) and ( r = 2 ). Thus, the calculation is ( \binom{4}{2} = \frac{4!}{2!(4-2)!} = \frac{4 \times 3}{2 \times 1} = 6 ). Therefore, there are 6 ways to choose 2 pens from 4.