BTGmoderatorLU wrote:Source: GMAT Paper Tests

If Mark saved an average (arithmetic mean) of $80 per week for 3 consecutive weeks, how much did he save the second week?

1) The average amount that Mark saved per week for the first 2 weeks was $60.
2) The amount that Mark saved the first week was 1/2 the amount he saved the second week and 1/3 the amount he saved the third week.

The OA is B

Let Savings in Month -1 is X, Month -2 is Y and Month -3 is Z

Sums of Savings for 3 months = Average * no: of months = 80*3 = $240 i.e X+Y+Z = 240

From (1) we know (X+Y)/2 = $60 X+Y = $120

We know X+Y+Z = $ 240 . from this we can find Z i.e that is savings of 3rd month which is $240-$120 = $120. But the infotmation is NOT Sufficient to get Y i.e savings of Month 2.

From (2) X= Y/2 , X=Z/3 i.e Z=3X i.e Z= 3Y/2

We know X+Y+Z = 240 . so we can substitute for value of Y to get savings of Month 2. Hence This information is Sufficient to get te answer.

Answer is B

PS Solving for Y we get Savings in Month 2 i.e Y/2+Y+3Y/2=240 6Y = 480 , Y = 80 . Savings in Month 2 = $ 80