In Mathematics: 30 is the sum of the first four squares, which makes it a square pyramidal number. It is also the sum of 2+4+6+8+10.
In History: One of the rallying-cries of the 1960s student/youth protest movement was the slogan, ‘Don’t trust anyone over thirty’.
In Sport: In tennis, the number 30 represents the second point gained in a game.
In the Bible: Jesus commenced ministry at 30 (Luke 3:23), Joseph was 30 when he stood before Pharaoh, King of Egypt (Genesis 41:46), King David was 30 when he began to reign (2 Samuel 5:4), and the Levites were numbered from the age of 30 and upward (1 Chronicles 23:3).
On the web: The Main Character in The Counting House game of basic arithmetic.
Once there was a man named Thirty. He loved to wander the wood and spend his days walking . He loved the sun and the sweet smell of the morning dew. One day the King stopped him on the road. “How many are you?!” Demanded the King. “Why I am not sure because no one has asked before!” answered Thirty. The king looked at Thirty and saw that he had three rows of ten but he wanted to be sure. He sent Thirty to his huge Counting House and demanded he be counted for! Please check for the King – roll the King’s royal dice and fill Thirty. How many coins did it take?