## Find the standard deviation of the thickness of an item.

1.  Two batteries, with voltages V1 and V2 , are connected in series. The total voltage V is given by V = V1 + V2 . Assume that V1 has mean 12 V and standard deviation 1 V, and that V2 has mean 6 V and standard deviation 0.5 V.

a.  Find μV . Assuming V1 and V2 to be independent,

b.  find σV .

2.   A laminated item is composed of five layers. The layers are a simple random sample from a population whose thickness has mean 1.2 mm and standard deviation 0.04 mm.

a.  Find the mean thickness of an item.

b.  Find the standard deviation of the thickness of an item.

3.  Two independent measurements are made of the lifetime of a charmed strange meson. Each measurement has a standard deviation of 7×10 −15 seconds. The lifetime of the meson is estimated by averaging the two measurements. What is the standard deviation of this estimate?

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