11. Gran's first grandchild guessed that Gran was 75 , the second 78 and the third 81 . It turned out that one of them was mistaken by 1 year, another one by 2 years and the other by 4 years. What is Gran's age?
A 76
B 77
C 78
D 79
E impossible to determine
SolUTION
E

Gran could be 77 (which is 1 below 78, 2 above 75 and 4 below 81 ). But she could also be 79 (1 above 78, 2 below 81,4 above 75). Hence it is impossible to determine her age from the information given.