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After two numbers are removed from the list $9,~13,~15,~17,~19,~23,~31,~49,$ the average and the median each increase by $2$. What is the product of the two numbers that were removed?

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Answer:

The removed numbers are 13 and 19, and the product is:

13*19 = 247

Step-by-step explanation:

We have the set:

{9, 13, 15, 17, 19, 23, 31, 49}

The original median is the number that is just in the middle of the set (in a set of 8 numbers, we take the average between the fourth and fifth numbers)

then the median is:

(17 + 19)/2 = 18

and the mean is:

(9 + 13 + 15 + 17 + 19 + 23 + 31 + 49)/8 = 22

We want to remove two numbers such that the mean and the median increase by two.

Is immediate to notice that if we want the median to increase by two, we need to remove the number 19 and one number smaller than 17.

Then the median will be equal to:

(17 + 23)/2 = 20

which is 2 more than the previous median.

because 19 assume that we remove the 19 and number N.

To find the value of N, we can solve for the new mean:

((9 + 13 + 15 + 17  + 23 + 31 + 49 - N)/6 = 22 + 2

(this means that if we remove the number 19 and the number N, the mean increases by 2.

(9 + 13 + 15 + 17  + 23 + 31 + 49 - N)/6 = 22 + 2

(9 + 13 + 15 + 17  + 23 + 31 + 49 - N) = 24*6 = 144

157 - N = 144

157 - 144 = N = 13

This means that the other number we need to remove is 13

Then we remove the numbers 13 and 19

The product of the two removed numbers is:

13*19  =247

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