7531 ⇒ (7 – 5) = (5 – 3) = (3 – 1) = 2 (The answer is 2 when the numbers are reduced to each other.) Similarly, it happens in 9753 and 8642. 2468 ⇒ (2 – 4) = (4 – 6) = (6 – 8) = – 2 (The answer is – 2 when the numbers are reduced to each other.) 2468 is different from the other options.