14.11. References 625
Exam Problems
Problem 14.70.
Each day, an MIT student selects a breakfast from amongbpossibilities, lunch
from amonglpossibilities, and dinner from amongdpossibilities. In each case
one of the possibilities is Doritos. However, a legimate daily menu may include
Doritos for at most one meal. Give a combinatorial (not algebraic) proof based on
the number of legimate daily menus that
bld Œ.b 1/C.l 1/C.d 1/C1ç
D.l 1/.d 1/C.b 1/.d 1/C.b 1/.l 1/C.b 1/.l 1/.d 1/: