Verbal Reasoning - Mental Ability Questions

What should come in place of the question mark (?) in the following number series?

8, 6, 9, 23, ?

Select the related word/letters/numbers from the given alternatives:

Summer : Aestivation :: Winter : ?

In the following question, select the missing number from the given series.

1, 3, 5, 7, ?

The following equation is incorrect. Which two signs should be interchanged to correct the equation?

5 + 8 ÷ 40 - 20 x 25 = 6

Select the related word/letters/number from the given alternatives.

COMMANDER : REDNAMMOC : : MANAGEMENT : ?

Select the related word from the given alternatives.

Examination : Success :: Matches : ___

Select the related word/letters/number from the given alternatives.

School: Study :: Laboratory: ?

Night blindness : Sight :: ___ : Speech