Consider three observations a, b, and c such that b = a + c. If the standard deviation of a + 2, b + 2, c + 2 is d, then which of the following is true?

The range of a$$\in$$R for which the

function f(x) = (4a $$-$$ 3)(x + log_e 5) + 2(a $$-$$ 7) cot$$\left( {{x \over 2}} \right)$$ sin²$$\left( {{x \over 2}} \right)$$, x $$\ne$$ 2n$$\pi$$, n$$\in$$N has critical points, is :

If for x $$\in$$ $$\left( {0,{\pi \over 2}} \right)$$, log₁₀sinx + log₁₀cosx = $$-$$1 and log₁₀(sinx + cosx) = $${1 \over 2}$$(log₁₀ n $$-$$ 1), n > 0, then the value of n is equal to :

A pack of cards has one card missing. Two cards are drawn randomly and are found to be spades. The probability that the missing card is not a spade, is :