GMATPrep 1 - question

Usually in GMAT problem,arithmetic operations are represented by some symbols.WE need to solve the equation.

Here a*b=a+b-ab[* refer to that symbol]

Option1:

a*b=a+b-ab

b*a=b+a-ba=a+b-ab

Both are same

Option2:

a*0=a+0-0=a

Bothe are same

Option 3:

Now take LHS

(a*b)*c

(a*b)=a+b-ab

(a+b-ab)*c=a+b-ab+c-(a+b-ab)c

=a+b+c-ab-(ac+bc-abc)

=a+b+c-ab-ac-bc+abc

Now take RHS

a*(b*c)

(b*c)=b+c-bc

a*(b+c-bc)=a+b+c-bc-a(b+c-bc)

=a+b+c-ab-ac-bc+abc

LHS=RHS.

Option 3 is also correct.

Hope this clarify....