There are 13 3-letter words listed below. For each of them, insert two letters between any one pair of letters in the word or at the end of the word (but not at the beginning), to form a 5-letter word. The two added letters must be adjacent to each other in the 5-letter word.
When complete, all 26 letters of the alphabet will have been used as fill-ins.
ant dim see
ass eel tie
bay far top
coy mar win
pie
What if the two letters were allowed at the beginning of the word? Try to find a few like that.
After trying for a long time to find the right combinations I resorted to writing a computer program to insert every possible pair of letters into every possible position (except in front) and then cross referencing the results with a database of english words. This gave me all the possible words that could be formed. I still had to use a fair bit of manual logic to figure out which words were the right ones, though. Here's what I came up with:
ANT + GS = ANGST
ASS + BY = ABYSS
BAY + WD = BAWDY
COY + MF = COMFY
DIM + EN = DENIM
EEL + XP = EXPEL
FAR + KI = FAKIR
MAR + JO = MAJOR
PIE + QU = PIQUE
SEE + RV = SERVE
TIE + TL = TITLE
TOP + AZ = TOPAZ
WIN + CH = WINCH
Lots of trial & error - resorting to computer help
