Let a # b = a*10 + b
Example :
5 # 5 = 55
9.5 # 3 = 98
Arrange numbers 1 to 7 to each piano's-white-keys.
Then arrange operators (+,-,x,/, and #) to each piano's-black-keys.
Operation is done from left to right.
(((((C op1 D) op2 EF) op3 G) op4 A) op5 B)
The result must be 3000.
(((((3/6) + 14) * 7) - 2) # 5) = 1000