If AB = 40, what is the value of AB(A + 2B)?
(1) A – B = -18.
(2) A( AB ) = 80.
As ans given “its B”
how A also satisfies the ans so it must be D
A-B = -18 and AB =40
so square(A+B )= square(A-B)+4AB
=> A+B = 22 not -22 as either A and B both will b negative or both will be positive since AB =40 and A-B = -18 show B >A so when B-A =18 , B is positive and A is positve so A+ B is positive.
so A+ B =22 and A- B =-18 , implies B = 20 and A=2
so AB (A+ 2B) =1680 same as option b gives.
Well
I feel that the Option A and the information AB = 40 doesn’t help me in
solving for any of the variables A or B , however we can be sure that
whatever can be the value of A or B (both -ve or both +ve) their
product is 40.
I strongly feel that only option B is sufficient and Not A, Therefore B.
to add to it
A-B = -18 signifies only the difference in variables not the nature
the variables i.e which one is positive / negative
IMO B, A is not suffi because A will gve 2 answers 20 and 2
D
Answer is B.
Option (2) gives us B=20 and A=2 by substituting.
AB(A+2B) = 1680.
Using option (1) we get A2(Square) +18A – 40=0 i.e. (A)(A-B)=-18(A)
Solving we get A=2 B=20 and A=-20 B=-2. Both satisfy the condition AB=40 and also A-B=-18. But when we try to find the value of AB(A+2B) we get 2 values i.e. 1680 and -960.
Hence option 1 is not sufficient/good enough.