Answer: 1/10
Step-by-step explanation:
Here, Total ticket = 2000
According to the question, ticket bought by Neil's group = 10 × 10= 100 ( because there are 10 person in group and each bought 10 tickets)
Therefore, Probability that Neil's group won the prize, P(G) = 100/2,000= 1/20
Now, The probability that Neil and group won, 
Thus, the probability that Neil won when it is found that Neil's group won,
=
= 1/10
Thus, P(N/G)= 1/10