Lucy earned $400 and $550 in interest the last 2 years. how much interest must she earn this year so that her average earnings over the three year period is more than $600? show your work.

the average of "arithmetic mean" of a dataset is simply the "sum of the data" divided by the "amount of data", so if we had say

a, b, c

its average will be (a+b+c)/3

so, let's say Lucy will need to earn "x" to have an average of $600, so

so, if she earns that much more, she'll have an average of 600, and if she earns more than that, her average is "more than 600" then.

x ⩾ 850.

square root

step-by-step explanation: