" -20 + 5p - 7z " is not a question, and it doesn't beg for an answer. It's an expression that stands for a number.
In order to determine what the number is, you need to know the values of 'p' and 'z'. And if either of those changes, then the value of " -20 + 5p - 7z " immediately changes too. So the whole thing is a 'moving target'.
<span>the proccess of choosing is independent so probability of choosing from machin1 is:300/1000 =0.3
choosing from machin2 is:707/1010=0.7 the total result is 0.3*0.7=0.21 ;</span>
