Verbal Reasoning - Mental Ability Questions

In the following question, by using which mathematical operators will the expression become correct?
27 ? 9 ? 18 ? 24 ? 12

A series is given, with one number missing. Choose the correct alternative from the given ones that will complete the series.

100, -20, 4, ? , 0.16, -0.032

Select the related word/letters/number from the given alternatives.
Nephrology : Kidney : : Ichthyology : ?

The average temperature of a town in the first six days of a month was 41 degC and the sum of the temperatures of the first five days of the same month was 201 degC. What was the temperature on the sixth day of the month?

Weight of Sona is four times that of Mona. Weight of Mona is 2.5 times of Hona. Weight of Hona is 1.5 times of Dhona. Weight of Dhona is 2.5 times of Rona. Who is the heaviest?

Select the related word/letters/number from the given alternatives.
EFGH: LNPR : : ABCD : ?

A series is given, with one term missing. Choose the correct alternative from the given ones that will complete the series.

XFB,UGD ,RIG ,OLK, ?

Select the missing number from the given responses: