What is black when it is clean and white when it is dirty?
= 5 + (5 x 7 )
= 12 x (12 - 7)
= 15 - (5 : 5)
= (4 x 12) - (12 x 2)
= 15 - 5 - 2 + 7
= (14 : 7) + 7
= 16 - (5 x 2)
= (24 : 4) x 2