Calculate the formula according to the meaning of the question:
Profit rate = profit/cost × 100%
= (selling price-cost) ÷ cost×100%
=(75-30)÷30× 100%
=45÷30× 100%
= 1.5× 100%
= 150%
Properties of mixed calculation:
In the mixed calculation, if there is only addition and subtraction or only multiplication and division, it is calculated from left to right, for example, 2+ 1- 1=2. First calculate the number of 2+ 1, and then subtract 1 from the number of 2+ 1. If the first-level operation and the second-level operation exist at the same time, the second-level operation is calculated first.
In multiplication calculation, the difference between two numbers is multiplied by a number, so that the minuend and the minuend can be multiplied by this number respectively, and then the product obtained can be subtracted. For example: (137-125) × 8 =137× 8-125× 8 = 96.