There are three varieties of sugar in a store

[guerrero]

There are three varieties of sugar in a store. Sugar (S1) costs $6 per kilogram and sugar (S2) costs $9 per kilogram. Sugar (S1) is mixed with Sugar (S2) and a new variety of Sugar (S3) is formed. If 20 kilograms of Sugar (S3) consists of A kilogram of Sugar (S1) and B kilogram of Sugar (S2), is A > B ?

(1) A > 9
(2) The cost of 20 kilogram of Sugar (S3) is more than $150.

OAB

[GMATGuruNY]

There are three varieties of sugar in a store. Sugar (S1) costs $6 per kilogram and sugar (S2) costs $9 per kilogram. Sugar (S1) is mixed with Sugar (S2) and a new variety of Sugar (S3) is formed. If 20 kilograms of Sugar (S3) consists of A kilogram of Sugar (S1) and B kilogram of Sugar (S2), is A > B ?

(1) A > 9
(2) The cost of 20 kilogram of Sugar (S3) is more than $150.

OAB

Since the weight of S3 is 20 kilograms, A+B = 20.

Statement 1: A > 9
It's possible that A=10 and that B=10, in which case A=B.
It's possible that A=11 and that B=9, in which case A>B.
INSUFFICIENT.

Statement 2: The cost of 20 kilograms of Sugar (S3) is more than $150.
If the cost of 20 kilograms is exactly $150, the average cost per kilogram = 150/20 = $7.5.
Since the total cost is actually MORE than $150, the average cost per kilogram must be MORE than $7.5 -- MORE THAN HALFWAY between A ($6) and B ($9).
For the average cost to be more than halfway between A and B, there must be MORE B THAN A in the mixture.
Thus, A < B.
SUFFICIENT.

The correct answer is B.