There are 16 points in a plane in which 6 are collinear. How many line...
There are 16 points in a plane in which 6 are collinear. How many line...
To find the number of lines that can be drawn by joining the given points, we need to consider two scenarios:
1. Lines formed by joining any two points
2. Lines formed by joining three or more collinear points
Lines formed by joining any two points:
In a plane, the number of ways to select 2 points out of 16 is given by the combination formula C(16,2) = 16! / (2!(16-2)!) = 16! / (2!14!) = (16 * 15) / (2 * 1) = 8 * 15 = 120.
However, we need to subtract the lines formed by joining the collinear points. Since there are 6 collinear points, we need to subtract the number of lines formed by joining these 6 points from the total.
Lines formed by joining three or more collinear points:
To find the number of lines formed by joining the collinear points, we can use the formula for combinations. The number of ways to select 3 points out of 6 is given by C(6,3) = 6! / (3!(6-3)!) = 6! / (3!3!) = (6 * 5 * 4) / (3 * 2 * 1) = 20.
Now, we subtract this number from the total number of lines formed by joining any two points: 120 - 20 = 100.
However, we have to consider that each line formed by joining three or more collinear points is counted three times in the total count of lines formed by joining any two points. Therefore, we need to add back these lines twice to get the correct count.
Adding back lines formed by joining three or more collinear points:
The number of lines formed by joining three or more collinear points is 20, and we need to add it back twice. Therefore, we add 2 * 20 = 40 to the count.
Final count:
120 - 20 + 40 = 140.
Thus, the number of lines that can be drawn by joining the given points is 140.
However, we have to keep in mind that we are counting each line twice (since we are considering pairs of points). So, we divide the count by 2 to get the final answer.
Final answer:
140 / 2 = 70.
Therefore, the correct answer is option A) 70.
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