"Book rules say that the same number is positive and different numbers are negative." It refers to multiplication and division between two numbers. Take your formula for example (-8 1) × 1? Negative sign; Then × (-4/5) with the same sign (both negative signs) is positive; Then × 16 is still the same number (both positive numbers) to get positive.

When calculating by multiplication and division, if there are numbers in brackets, the positive sign is directly removed from brackets and symbols, and the negative sign is counted when the brackets and symbols are removed. Odd numbers are negative and even numbers are positive. For example, the next step of (-3)x(+ 1/2)x(-8) is 3x0.5x8, because there are two negative signs and even numbers of results are positive.