31.   They would be great intellectual challenges.

32.   To keep his brain stimulated, he also takes on a new intellectual challenge about once every five years, among them learning French, statistics and brain biology.

33.   What keeps the students motivated is their love of games, combined with the intellectual challenge of game design.

34.   She said she likes the intellectual challenge of singing.

35.   One who enjoys the intellectual challenge of creatively overcoming or circumventing limitations.