his math is not correct. the expression he's looking for is:
2/50 + (2/49 * 48/50) + (2/48 * (1 - (2/50 + (2/49 * 48/50)))) = 0.04 + 0.039 + 0.0383 = 0.1173, not the 0.122 that he came up with. in this case, it happens to be close, but this type of error is common and can be costly.