NumberWiz examples

NumberWiz can present quite some challenges. 


Here's an example. How do you apply addition, subtraction, multiplication and division to make the number 390 out of the numbers 3 7 8 9 75 100 ?
A solution: (8-3) x 9 x 7 + 75 = 5 x 67 + 75. Creativity certainly helps.


How then do you make the number 640 out of the numbers 6 7 8 9 9 50 ?
One solution is: ((9x9) - (7-6)) x 8 = 80 x 8 = 640. Less difficult than the previous.