What was the percent increase in the average (arithmetic mean) contrib

Let’s say that the average contribution at 1985 be A, and number of members be B, and the average contribution at 1995 be X, and number of members be Y.

The percentage increase in the average contribution per member from 1985 to 1995 = [{(X/Y)—(A/B)}/(A/B)]*100= \({\frac{BX}{AY}-1}*100\)

We don’t know B and Y from the statement (1).

We don’t know A and X from the statement (2).

However, we can fine the value when we consider both (1) and (2) together.

Statement (2) gives us the information that Y=2B. Therefore, \({\frac{BX}{2BA}-1}*100={\frac{X}{2A}-1}*100={\frac{1,225,890}{2*505,210}-1}*100≈21.3\)

Therefore both statements together are sufficient, but neither statement alone is sufficient.


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