# A factory makes a large number of ropes with lengths either 3 m or 5 m. ?

A factory makes a large number of ropes with lengths either 3 m or 5 m. There are four times as many

ropes of length 3 m as there are ropes of length 5 m.

One rope is chosen at random. Find the expectation and variance of its length

The answer for expectation is 3.4 but how to find it?

Thanks

### 1 Answer

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- PuzzlingLv 72 months agoFavorite Answer
Imagine a representative sample of 4 ropes (3m) and 1 rope (5m).

Calculate the total length:

(4 * 3) + 5 = 17

Divide by 5 ropes in the representative sample:

17/5 = 3.4

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