2. A sample 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):

T T H T C T T S C H S S T H C T T T H T

a. Estimate the true proportion of all such students who own a Texas Instruments calculator.

b. Of the 10 students who owned a TI calculator, 4 had graphing calculators. Estimate the proportion of students who do not own a TI graphing calculator.