Me need

the following numerically ordered sequence of number's has a mean of 17 and a median of 18.
7,a,12,15,17,b,20,22,24,25
given this information, the values of a & b must be

Dexter read 11 science fiction books and 5 history books. lena read 9 science fiction books and 4 history books. compare the students’ ratios of science fiction books to history books. 1. determine the ratios’ form:    science fiction books to history books 2. write the ratios as fractions:    dexter: 115; lena: 94 3. rewrite with a common denominator. 4. compare. 5. answer the question. determine which shows the correct comparison of the ratios for this problem.