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What ia the sum if the first 7 terms of the geometric series

The random variable x has probability density function f (x) = k(−x²+5x−4) 1 ≤ x ≤ 4 or =0 1 show that k = 2/9 find 2 e(x), 3 the mode of x, 4 the cumulative distribution function f(x) for all x. 5 evaluate p(x ≤ 2.5). 6 deduce the value of the median and comment on the shape of the distribution.

Arectangle has a perimeter of 20 cm. the length, x cm, of one side of this rectangle is uniformly distributed between 1 cm and 7 cm. find the probability that the length of the longer side of the rectangle is more than 6 cm long.