To give you an idea of what we want, the following would be an acceptable answer for the question asked:
Explain briefly (at most a few sentences!) how we
know that the probability of detecting an electron may be described as
a superposition of waves of wavelength 
, where h is
Planck's constant and p is the momentum of the electron. Be sure to
explain both the superposition and the formula for 
.
Hints: For your convenience, a list of experiments is
provided on the last page of the formula sheet. Be brief and save
yourself time for the rest of the exam.