Let cost of buying 6 chairs in sets = Cs
Let cost of buying 1 chairs individually = Ci
Let cost of buying 6 chairs individually = 6Ci


Given Cs < 6Ci

TO FIND : Cs

Stmt I

Cs = .90* (6*Ci)

INSUFF
We just know the relation BETWEEN Cs & Ci.Dont know the exact costs.

Stmt II
Cs + 20 = 5Ci


INSUFF
We just know the relation.Dont know the exact costs

Stmt I and II together

SUFFICIENT

Cs = .90* (6*Ci) (1)

Cs + 20 = 5Ci (2)

SUBSTITUTE Cs = .90* (6*Ci) IN (2)

We can solve for Ci and then Cs. No need to calculate since its a DataSufficiency question

Choose C)

Hope this helps! Let me know if u still hv questions.

Thanks cramya. But I had calculated the equations and not found a solution and then selected E. "No need to calculate is the key for me"

Good solution Cramya. One small correction.

Stmt II
Cs + 20 = 5Ci should be

Stmt II
Cs = 20 + 5Ci

Though not affecting answer.

Ans is still C .