Assuming that addition and subtraction are the only allowable operations, we can see that the equality cannot be realised, because on the left-hand side there are an even number of even numbers and an odd number of odd numbers. No combination of addition and subtraction can produce an even number. So if brackets are used to group the operands on the left, the result will nevertheless be an odd number, and the right-hand side is even.
The next plan is to change the base of the numbers to the lowest odd number. The largest digit is 5. The nearest odd number to 5 is 7. Therefore 10 represents the decimal number 7. So to base 7 we have 5 odd numbers and two even numbers. The result will therefore be odd. But this time the right-hand side is odd, because 10 represents the number 7. The sum becomes 7-5+4+1-7+5-2=7, which is still not correct. But if we insert brackets to group some of the numbers together we can write: 7-(5+4+1-7)+5-2=7. This is an exact equation. The three 7's can now be replaced by 10 and the equation interpreted by calculating in base 7 instead of in decimal.