The average life of a bread-making machine is 7 years, with a standard deviation of 1 year. assuming
that the lives of these machines follow approximately a normal distribution, find
(a) the probability that the mean life of a random sample of 9 such machines falls between 6.4 and 7.2 years;
(b) the value of x to the right of which 15% of the means computed from random samples of size 9
would fall.

the law of definite proportions states samples of a compound will always contain the same proportion of elements by mass. in other words, a given compound will always contain the same elements in the same proportions by mass.the law of multiple proportions states when two elements combine with each other to form more than one compound, then the weights of one element that combine with a fixed weight of the other are in a ratio of small whole numbers.