Draw out a number line with the values 0, 5, 10, 15, 20, 25, 30, etc (basically multiples of 5)
Then plot a point at 25
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Or you can draw out a number line with the multiples of 10, so with the values 0, 10, 20, 30, ...
Then plot a point at the exact midway point between 20 and 30 to represent the value 25
You would subtract the atomic number from the mass weight. <span />
The way to do this is by using PEMDAS. P (parentheses) E (exponents) M (multiplication) D (division) A (Addition) S (subtraction). The answer would be -1539
