Aresearcher posts a magazine advertisement offering $30 in exchange for participation in a short study. the researcher accepts the first three people who respond to the advertisement. which of the following statements is true about the sample?

a. it is not a valid sample because it is not a random sample of the population.
b. it is a valid sample because the first three people were selected to participate. c. it is a valid sample because money was offered to participants.
d. it is not a valid sample because it is only a short study.

Ateacher has $80 to buy workbooks. each work book cost $3. if she buys as many workbooks as possible, how much money does she have leftover? a) $2 b) $4 c) $6 d) $8

To find the extreme values of a function f(x. y) on a curve x-x(t), y y(t), treat f as a function of the single variable t and use the chain rule to find where df/dt is zero. in any other single-variable case, the extreme values of f are then found among the values at the critical points (points where df/dt is zero or fails to exist), and endpoints of the parameter domain. find the absolute maximum and minimum values of the following function on the given curves. use the parametric equations x=2cos t, y 2 sin t functions: curves: i) the semicircle x4,y20 i) the quarter circle x2+y-4, x20, y20 b, g(x, y)=xy

Tom had a total of $220 and he spent $35 on a basketball ticket . what percent of his money did he have left?