请教数学题,麻烦牛牛帮忙解答一下

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In the xy-plane, does the line with equation y=3x+2 contain the point (r, s)?
(1) (3r+2-s)(4r+9-s)=0
(2) (4r-6-s)(3r+2-s)=0
Ans: ( c )

At a dinner party, 5 people are to be seated around a circular table. Two seating arrangements are considered different only when the positions of the different relative to each other. What is the total number of different possible seating arrangements for the group?
A. 5
B. 10
C. 24
D. 32
E. 120
Ans: C. 24

Linda put an amount of money into each of two new investments, A and B, that pay simple annual interest. If the annual interest rate of investment B is 3/2 times that of investment A, what amount did Linda put into investment A?
(1) The interest for 1 year is $50 for investment A and $150 for investment B.
(2) The amount that Linda put into investment B is twice the amount that she put into investment A.
Ans: E

The residents of Town X participated in a survey to determine the number of hours per week each resident spent watching television. The distribution of the results of the survey had a mean of 21 hours and a standard deviation of 6 hours. The number of hours that Pat,, a resident of Town X, watched television last week was between 1 and 2 standard deviations below the mean. Which of the following could be the number of hours that Pat watched television last week?
A. 30
B. 20
C. 18
D. 12
E. 6
Ans: D. 12 Why?