11. Dad says he is exactly 35 years old, not counting weekends. How old is he really?
A 40
B 42
C 45
D 49
E 56
SolUtion
D

Since Dad is excluding weekends, he is only counting $\frac{5}{7}$ of the days. Therefore 35 is $\frac{5}{7}$ of his real age. Hence his real age is $35 \times \frac{7}{5}=49$.