Answer:
Answer: E
Helen, a high school teacher, wants her students to actively participate more in class. She has decided to use reinforcement theory to get the required results. Which of the following methods is she most likely to use?
.a) She is going to call on students who never participate
.b) She is going to yell at students, telling them that they are not making good grades
.c) She is going to ask the students that always participate to allow the others to have a chance
.d) She is going to model what active participation should look like ,at the beginning of class
.e) She is going to give students extra credit each time that they contribute.
Establishing a link between malpractice and harm is a link distinction
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Answer:</h3>
60 days
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Explanation:</h3>
Half-life is the amount of time it takes half of a substance to decay away.
Guess and Check
One method for solving half-life problems like this is to guess and check. To do this, we can continue to divide 475mg by 2 until we get to 30mg.
- 475 ÷ 2 = 237.5
- 237.5 ÷ 2 = 118.75
- 118.75 ÷ 2 = 59.375
- 59.375 ÷ 2 = 29.6875
As seen here, it takes approximately 4 half-lives for this sample of Ra-225 to decay to 30mg. Now, we can multiply 4 by the length of the half-life, 15 days.
Fractions
Another way to solve this is to use fractions.
- 16 is equivalent to
.
This means that it takes 4 half-lives for 475mg to decay to 30mg. Using the same method above, we can tell that 4 half-lives are 60 days.
Important Note
In this question, I rounded occasionally. So, not all of the values are exact, but they are all very close.