Karishma123 wrote:Hi All

I have attached the question (see attachment) - its from GMAT prep test 1

Need help - my exam is around the corner


According to me the ans should be B
But GMAT prep is giving ans A

The question asks: Does (6∆2)∆ 4 = 6∆(2∆4)?

If ∆ = addition:
Does (6+2) + 4 = 6 + (2+4)?
8+4 = 6+6
12 = 12. Yes.

If ∆ = subtraction:
Does (6-2) - 4 = 6 - (2-4)?
4-4 = 6-(-2)
0 = 8 No.

If ∆ = multiplication:
Does (6*2) * 4 = 6 * (2*4)?
12*4 = 6*8
48 = 48 Yes.

If ∆ = division:
Does (6/2)/4 = 6/(2/4)?
3/4 = 6/(1/2)
3/4 = 12 No.

So, looking at the question Does (6∆2)∆ 4 = 6∆(2∆4)?

If ∆ = addition or multiplication, the answer is YES.
If ∆ = subtraction or division, the answer is NO.

Statement 1:
3+2>3. This works. ∆ could represent addition.
3-2>3. Doesn't work. ∆ cannot represent subtraction.
3*2>3. This works. ∆ could represent multiplication.
3/2>3. Doesn't work. ∆ cannot represent division.

So ∆ could represent addition or multiplication
As noted above, if ∆ = addition or multiplication, the answer is YES.
Sufficient.

Statement 2:
3*1=3. This works. ∆ could represent multiplication.
3/1 = 3. This works. ∆ could represent division.

So ∆ could represent multiplication or division.
As noted above:
If ∆ = multiplication, the answer is YES.
If ∆ = division, the answer is NO.
Since the answer can be both YES and NO, insufficient.

The correct answer is A.