Question

Three numbers have a mean of 64.when a fourth number is included the mean is doubled. What is the
fourth number?

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Answer 1

Step-by-step explanation:

Let us represent the four numbers as a, b, c, and d with d as the fourth number. Take note that average is the total sum divided by the quantity. We can then represent the given as the following equations,

(a + b + c) / 3 = 64

(a + b + c + d) / 4 = 64

We can remove the denominators by multiplying both sides by it,

(a + b + c) = 64 * 3

(a + b + c + d) = 64 *4

We can take the difference of the two sums to only get d,

(a + b + c + d) - (a + b + c) = 64 * 4 - 64 * 3

d = 64 (4 - 3)

d = 64 (1)

d = 64