Answer: The required ratio of people to T-shirts sold is 5 : 1.
Step-by-step explanation: Given that one T-shirt is sold for every 5 people who attend a concert.
We are to find the ratio of people to T-shirts sold.
Let 1x represents the number of total T-shirts sold and 5x be the number of people that attended the concert.
Therefore, the ratio of people to T-shirts sold is given by

Thus, the required ratio of people to T-shirts sold is 5 : 1.