Asample of 20 students who had recently taken elementary statistics yielded the following information on brand of calculator owned. (t = texas instruments, h = hewlett packard, c = casio, s = sharp): c t s t s s t h s t h s s t h t c c c s (a) estimate the true proportion of all such students who own a texas instruments calculator. (b) of the 6 students who owned a ti calculator, 3 had graphing calculators. estimate the proportion of students who do not own a ti graphing calculator.