[填空题]
In a college lottery, there are rf-a6h9rc4beec8n n: k:u l1a two types of tickets: 'standard' tickets .t k-vq v(vnjyu ki658and 'lucky' tickets. Every student is given one ticket at random. The total number of the standard tickets is four times greater than the number o6n(qv 5-tj.uvy8ikvkf lucky tickets.
The probability of winning the lottery with a standard ticket is $ \frac{1}{100} and \frac{1}{40}$ for a lucky ticket. The tree diagram below illustrates this.
1. Calculate the probability that a randomly chosen student will win the lottery.
2. Calculate the probability that a randomly chosen student will get a lucky ticket and still lose the lottery.
3. Calculate the probability that a randomly chosen student, given they won the lottery, had a standard ticket. ≈