1, The same three-letter word can be inserted into the blanks below to form complete words.

T _ _ _ K
P _ _ _ E
B _ _ _ T
B _ _ _ CH
SC _ _ _ CH

2.  The same two letters, in the same, consecutive order, will change each word below into a new one. One of the new words is hyphenated.

SIN
TAN
VISOR
CIRCUS

HINTS:
2)
#1: The two letters make up a word.
21: The two letters are inserted into each clue word.
#3. The two letters could be added to PERM and BAND.


Answers:

1. The three-letter word is RUN:

TRUNK
PRUNE
BRUNT
BRUNCH
SCRUNCH 

2. The two letters are IT:

SIT-IN
TITAN
VISITOR
CIRCUITS
(PERMIT / BANDIT)

Credit: Puzzle #2
NY Times Crossword - Feb. 18, 2007
David Kwong and Kevan Choset
MAGIC WORDS  (Now you see it, now you don't.)