An unbiased die is thrown three times; the sum of numbers coming up is 10. The probability that two has appeared at least once is:
D 1/18 ?
I was able to find out of 216 possible outcomes of throwing dice thrice only 27 of them give sum ten. Then I counted number of triads where no 2 was there which were 17 and hence the required probability should be 10/27? Where am I making a mistake?