Suppose you want to make a certain kind of tropical punch using bananas, oranges, and papayas. This is what you know.
You know the recipe takes seven pieces of fruit.
You don't know how many of each to put in the punch, but you know that
there are twice as many oranges as bananas.
You know that the seven pieces of fruit cost $5.25, where bananas cost $.50
each, oranges cost $.75 each, and papayas cost $1.25 each.
How many pieces of each type of fruit do you need to make the tropical punch?

4 oranges, 2 bananas, and 1 papaya

Step-by-step explanation:

because there are twice as many oranges as bananas and 7 total fruit so 4 is the max amount of oranges you can have which leaves 2 bananas and 1 left over which is the papaya. Then to check work plug in the amount of fruit times their price which totals $5.25.

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