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Poster has been reminded to post schoolwork in the Homework Help forums

**Summary::**When filling up carts with iron the real weight deviates from the nominal value 10 ton. The standard deviation is .5.

What's the probability that 25 carts exceed 255 ton?

The arithmetic median value is:

$$X \in N(25 * 10, 0.5 / \sqrt{25}) = N(250, .1)$$

$$P(x > 255) = 1 - P(x < 255) $$

$$1 - Φ( \frac {255 - 250} {.1} ) = 1 - Φ(50) \approx 0$$

The book says answer is 1 - Φ(2)

but i see no way of that being true.