you find the blank number by finding the pattern. on number 9 the number increases by 10 every time. you find the mean by adding all the numbers on question 9 and finding the average.
example say its 0 5 10 _ 20 25
you can assume the blank is 15 because the pattern is +5
then you add all of them together which is 75
then you find the average or mean. you find this by dividing it by the numbers you started off with. with this example you divide it by 6 because we started with 6 numbers.
