State whether the selection described below is a combination or a permutation. (You do not have to compute the value.)
Josephine chooses three of six textbooks to take with her on vacation.

Find the gradient of f(x, y,z)equals=left parenthesis x squared plus y squared plus z squared right parenthesis superscript negative 1 divided by 2 baseline plus ln left parenthesis x right parenthesis x2+y2+z2−1/2+ln(xyz) at the point left parenthesis negative 2 comma 1 comma negative 2 right parenthesis(−2,1,−2).

On the first of each month sasha runs a 5k race she keeps track of her times to track her progress her time in minutes is recorded in the table

Charlie tosses five coins. what is the probability that all five coins will land tails up.