2. In a class of80 students in University, 45 are in mathematics, IS are good in both mathematics and in English, 13 are good in both mathematics and psychology, 16 are good in both English and psycholoo' only, 20 are good in psychology and 9 are good in of the three courses. 2pts. eaeb a) How many students are good in mathematics only? b) How many students are not good in any of the three course?

Ariana starts with 100 milligrams of a radioactive substance. the amount of the substance decreases by 20% each week for a number of weeks, w. the expression 100(1−0.2)w finds the amount of radioactive substance remaining after w weeks. which statement about this expression is true? a) it is the difference between the initial amount and the percent decrease. b) it is the difference between the initial amount and the decay factor after w weeks. c) it is the initial amount raised to the decay factor after w weeks. d) it is the product of the initial amount and the decay factor after w weeks.