How do i find the value of x geometry is killing me right now

Standard deviation of 19,29,21,22,23

Which of the following is the explicit rule for a geometric sequence defined a recursive formula of a -5a for which the first term is 23?

Serena is making an experiment. for that, she needs 20 grams of a 52% solution of salt. she has two large bottles of salt water: one with 40% and the other with 70% of salt in them. how much of each must she use to make the solution she needs? i am in need of