Set P consists of 10 positive integers arranged in order of increasing...
Given:
- Set P is an arithmetic sequence with common difference(d) = 4 and number of terms(n) = 10
- Let the first term be a.
- So, the other 9 terms = {a+d, a+2d, ……a+9d}
- (a+9d) and (a+8d) are removed
To Find: Decrease in the average of the set after removal of (a+9d) and (a+8d)
Approach:
- To calculate the decrease in the average of the sequence, we need to calculate the average of the sequences before and after removal of the terms (a+9d) and (a+8d)
- Calculating Average of the original set P
- As we know all the terms of the set P in terms of a, we can calculate the sum of all the terms in set P using the sum of an arithmetic sequence formula.
Once, we know the sum of an arithmetic sequence P, we can calculate the average of the arithmetic sequence by dividing the sum by the number of terms(i.e. 10)
- Calculating Average of set P after removal of (a+9d) and (a+8d)
- The new sum of the arithmetic sequence can be calculated by subtracting the sum of (a+9d) and (a+8d) from the original sum of the arithmetic sequence
- The new average can then be calculated by dividing the new sum by the remaining terms in the sequence(i.e. 8)
Working out:
- Calculating Average of the original set P
Hence, the average decreased by 4 units.
Answer : C
View all questions of this test
Set P consists of 10 positive integers arranged in order of increasing...
Given information:
- Set P consists of 10 positive integers arranged in order of increasing magnitude.
- The difference between any two successive terms of the set is 4.
- The two largest terms of the set are removed.
To find:
The decrease in the average (arithmetic mean) of the set after removing the two largest terms.
Solution:
Let's assume the smallest term in the set as x. Since the difference between any two successive terms is 4, we can represent the set as follows:
x, x+4, x+8, x+12, x+16, x+20, x+24, x+28, x+32, x+36
Step 1: Find the sum of all terms in the original set.
Sum = x + (x+4) + (x+8) + (x+12) + (x+16) + (x+20) + (x+24) + (x+28) + (x+32) + (x+36)
Sum = 10x + 180
Step 2: Find the average of the original set.
Average = Sum/Number of terms = (10x + 180)/10 = x + 18
Step 3: Remove the two largest terms from the set.
Since the two largest terms are x+36 and x+32, the new set will be:
x, x+4, x+8, x+12, x+16, x+20, x+24, x+28
Step 4: Find the sum of all terms in the new set.
Sum = x + (x+4) + (x+8) + (x+12) + (x+16) + (x+20) + (x+24) + (x+28)
Sum = 8x + 120
Step 5: Find the average of the new set.
Average = Sum/Number of terms = (8x + 120)/8 = x + 15
Step 6: Find the decrease in the average.
Decrease in average = Original average - New average
Decrease in average = (x + 18) - (x + 15)
Decrease in average = 3
Therefore, the decrease in the average of the set after removing the two largest terms is 3.