A box contains 10 blue pens and 10 red pens. Without looking, mrs. Perez selects a pen, uses it, and returns it to the box. Then go back and get another pen to use. What is the probability that Mrs. Perez chooses a red pen first and then a blue pen?

marco saved more.   he saved $35 more.

step-by-step explanation:

1+2+3+4+5+6+7+8+9+10 = 55

2*10 = 20

55-20 = 35

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

b.

step-by-step explanation:

i just know