Solution
Let his scores in ascending order be a1, a2, a3, a4, a5 and a6.
Since lowest score is 70, a1 = 70.
We need to know whether (a1+a2+a3+a4+a5+a6)/6 < 80 or not.
Or whether (a1+a2+a3+a4+a5+a6) < 480 or not.
Or whether a2+a3+a4+a5+a6 < 410 or not.
Consider first (1) alone.
It means (a1+a2+a3)/3 = 72.
Or (a1+a2+a3)=216
Or (a2+a3)=146.
So we need to know whether a4+a5+a6<{410 - 146=264} or not .
Since a1 = 70 is the lowest score we can only say that a4>70, a5>70, a6>70 or (a4+a5+a6)>210.
But we cannot say whether (a4+a5+a6) < 264 or not.
So (1) alone is not sufficient.
Next consider (2) alone.
It means (a4+a5+a6)/3 = 92.
Or (a4+a5+a6) = 276.
So we need to know whether (a2+a3) < {(410-276) = 134} or not.
Now a2 > (a1=70) and a3 > (a1=70).
So a2+a3>140.
Or a2+a3 is definitely not < 134.
So from (2) we can say that average of 6 quizzes is not less than 80.
Hence (2) alone is sufficient to answer the question.
The correct answer is (B).