A20% acid solution is mixed with a 70% acid solution to get 50 liters of a 40% solution. which of the following expressions is equal to 4(50)?
a.) 0.2x + 0.7y
b.) 2x + 7y
c.) x + y

in 1859, charles darwin set out his theory of evolution by natural selection as an explanation for adaptation and speciation. he defined natural selection as the "principle by which each slight variation [of a trait], if useful, is preserved".