In a bag containing 3 black balls and 2 red balls , a ball is picked at random then replaced. A second ball is chosen. What is the probability of :

I. both balls being black II. one is black ,the other is red.

2.in a class of 22 boys and 18 girls , two students are to be selected .
What is the probability of selecting two students of the same sex.​

Define multiplicative inverse. give an example of a number and its multiplicative inverse.

What is the value of x when x + 7 = 21?

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.