Cindy wore 3417.
Lisa wore 5216.
Maria wore 5500.
Tommy wore 5328.
Zack wore 5330.

Step 1
List the numbers from lowest to highest:
3,417
5,216
5,328
5,330
5,440

Step 2
Use the clues.

• Cindy had the lowest number.
  Cindy's number must be 3,417.
• The digit in the tens place on Tommy's shirt is one more than the digit in the tens place on Cindy's shirt.
  Cindy's number is 3,417. One more than 1 is 2. The only number with a 2 in the tens place is 5,328. Tommy's number must be 5,328.
• Maria was the last person to sign in for the race.
  There were 5,500 people in the race.
  Maria's number must be 5,500.
• Zack and Tommy were closest to each other in line.
  The second clue proved that Tommy's number is 5,328.
  The number closest to 5,328 is 5,330.
• Lisa's number is lower than Tommy's.
  Tommy's number is 5,328. The only number that is left without an owner is 5,216. That is lower than Tommy's. It must be Lisa's.