2.34 Irrelevant speech effects. In a psychological study of short- D ISR term memory, irrelevant speech effects refer to the degree to which the memorization process is impaired by irrele- vant background speech (for example, trying to memorize a list of numbers while listening to a speech in an unfa- miliar language). An analysis of irrelevant speech effects was carried out and published in Acoustical Science & Technology (Vol. 35, 2014). Subjects performed the mem- orization 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. Histogram of RDER Frequency 20- 18- 16- 14- 12- 10- 8- 6- -45 -15 15 45 75 105 135 165 195 225 255 . RDER Value a. Convert the frequency histogram into a relative fre- quency 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?