Suppose that x1 and x2 are i. i.d. random variables and that each of them has the uniform distribution on the interval [0, 1]. find the p. d.f. of y = x1 + x2.

The half-life of a certain material is 0.002 second. approximately how much of a 14-gram sample will be left after 0.004 second? a. 12 grams b. 3.5 grams c. 0.06 gram d. 7 grams