In a psychological study of short term memory, irrelevant speech effects refer to the degree to which the memorization process is impaired by irrelevant background speech For example, trying to memorize a list of numbers while listening to a speech in an unfamiliar language). An analysis of irrelevant speech effects was carried out and published in Acoustical Science & Technology (Vol. 35, 2014). Subjects performed the memorization task under two conditions: (1) with irrelevant background speech and (2) in silence. The difference in the error rates for the two conditions-called the relative difference in error rate (RDER)-was computed for each subject. A MINITAB histogram summarizing the RDER values for 71 subjects is displayed here.

a. Convert the frequency histogram into a relative frequency histogram.
b. What proportion of the subjects had RDER values between 75 and 105?
c. What proportion of the subjects had RDER values below 15?

Histogram of RDER 20- 18- 16- 14- 12- 10- 8- - 4- 2- 0- -45 -15 15 45 75 105 135 165 195 225 255 RDER Value Prequency