12.) your mother gave you $13.32 with which to buy a present. this covered 3/5 of the cost. how much did the present cost?

13.) if the weight of a package is multiplied by 5/7 the result is 40.5 pounds. find the weight of the package.

14.) a stray dog ate 12 of your muffins. that was 3/10 of all of them! with how many did you start?

not only in mathematics, scientific proof also are required in the other field of science. also maths proofs are of particular structure, containing steps and logics. so proving is like doing science, it is science. that's why it is important to prove. 

an inaccurate proof leads to errors, or stating results that are not accurate.  which wil mess the probelm up you dont want this