STUMPERS CCXV

Credit: NPR Weekend Edition Sunday Puzzle
May 27, 2012
Peter Persoff
Presented by Will Shortz

Think of two common words, one of three letters and the other of five. If you add the same two letters to the beginning of both words, you will have the present and past tense of a common verb. What are the two words, the two-letter prefix, and the new words?

HINT:
One of the words in the instructions above should help you.

Answer:

The words are INK and OUGHT.
Adding the letters TH to the beginning of each word gives THINK and THOUGHT.