Arnold and Danny are two twin brothers that are celebrating their birthday. The product of their ages today is smaller by 13 from the product of their ages a year from today. What is their age today?	Choose the correct answer.
A) 2 . B) 6 . C) 5 . D) 7 . E) 9 .

Rationale: ad = ( a + 1 ) ( d + 1 ) - 13 0 = a + d - 12 a + d = 12 a = d ( as they are twin brothers ) a = d = 6 b is the answer
Answer: B