So, this is a proportion problem. If we express 75% as a fraction (3/4ths), we have:
Since he won all of his games, we add the number won (x), to the number previously won and divide it by the total games played which is just the previous games played plus the number of current games played, so since he lost no games we still add x to the denominator as well. Solving this gives us:
That x value is 20.
Answer:
And we can assume a normal distribution and then we can solve the problem with the z score formula given by:
And replacing we got:
We can find the probability of interest using the normal standard table and with the following difference:
Step-by-step explanation:
Let X the random variable who represent the expense and we assume the following parameters:
And for this case we want to find the percent of his expense between 38.6 and 57.8 so we want this probability:
And we can assume a normal distribution and then we can solve the problem with the z score formula given by:
And replacing we got:
We can find the probability of interest using the normal standard table and with the following difference: