Method to use all the numbers in a string to equal other number

[ginyu]

I was recently given the challenge to take a string of numbers (ages) and + x - / to equal another number (age). As part of the challenge each number can only be used once and you must only use numbers here to do multiply, add to, subtract from or divide by.

NUMBERS
7 9 11 37 45 45 47 75
TARGET NUMBER
70

Im not looking as much for the answer, more if there is any efficent method to do this rather than guess and check

 

[Office_Shredder]

Do you have to use each number once, or can I omit some of them from the solution?