Suppose we have a bag with 10 slips of paper in it. Eight of these have a 2 on them and the other two have a 4 on them. How many 4's do we have to add to make the expected value equal to 3?

2 * [ 8 / (10 + x) ] + 4 [ x + 2] / [10 + x] = 3

Where x is the number of additional slips showing "4"

Simplify the above.....and we get

[ 16 + 4x + 8 ] / [ 10 + x ] = 3

24 + 4x = 3 [ 10 + x ]

24 + 4x = 30 + 3x

x = 6