7. Peter Piper picked a peck of pickled peppers. 1 peck $=\frac{1}{4}$ bushel and 1 bushel $=\frac{1}{9}$ barrel. How many more pecks must Peter Piper pick to fill a barrel?
A 12
B 13
C 34
D 35
E 36
Solution: D
We have 1 barrel $=9$ bushels and 1 bushel $=4$ pecks, and so 1 barrel $=9 \times 4=36$ pecks. Peter Piper has already picked 1 peck, so he needs to pick 35 more pecks to fill a barrel.