Well, some of the questions did not have their answers as part of the selectable options and some correct answers were regarded as incorrect.

for example.
A rectangle has a length of 10 cm and width of 6 cm. What is the perimeter of the rectangle? 

Perimeter is the total distance around the rectangle i.e. 2x(L+W), translating to 2x(10+6) = 2x16 =32cm.
But 32cm was not the correct answer.