Multiple answers possible here – if balls are same size and weight probability = 390/26 = 1 in 15.

if balls have other unique identifying feature such as different size etc that you know about in advance a can feel the difference then odds can increase up to certainty.

There are 20

09,19,29,39,49,59,69,79,89,90,91,92,93,94,95,96,97,98 is 18 and 99 is another two to make a total of 20.