由 vantreal » 2007-11-02 06:38
the average =30 and the sum of four numbers=120
(1) None of the four numbers is greater than 60.
if there are four 30s, then there's NO number greater than 30.
if there are three 10s, then there's 90 as the fourth number.
-> ONE number is greater than 30
---> insufficient
(2) Two of the four numbers are 9 and 10, respectively.
since the sum of four numbers=120,
and Two of the four numbers are 9 and 10,
and sum of the rest of two numbers must be 120-9-10=101
there are many possibilities, such as 1and 100, 50and 51.
we still cannot determine how many numbers are greater than 30.
---> insufficient
(1)+(2)
since none of the numbers is greater than 60.
we can assume that,
for (2) the sum of the rest of two numbers=101,
the greater number is 60, then the rest number is 51.
other possibilities include (59,52), (58,53), (57,54),(56,55),(55,56),(54,57),(53,58),(52,59),(51,60)
therefore, we can know there are TWO numbers greater than 30.
---> sufficient
Ans: (C)