Suppose the average weight of9 persons is 50 kg. The average weight of...
Weight of fifth person = (5 × 45 + 5 × 55) – 9 × 50
= (225 + 275) – 450
= 500 – 450 = 50 kg
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Suppose the average weight of9 persons is 50 kg. The average weight of...
Given Information:
- The average weight of 9 persons is 50 kg.
- The average weight of the first 5 persons is 45 kg.
- The average weight of the last 5 persons is 55 kg.
To find: The weight of the 5th person.
Solution:
Let's assume the weight of the 9 persons are as follows -
- w1, w2, w3, w4, w5, w6, w7, w8, w9
Now, we can use the formula for the average weight of n persons, which is:
Average weight of n persons = (Sum of weights of all persons) / n
Using this formula, we can write the following equations -
- (w1 + w2 + w3 + w4 + w5 + w6 + w7 + w8 + w9) / 9 = 50 (Average weight of 9 persons is 50 kg)
- (w1 + w2 + w3 + w4 + w5) / 5 = 45 (Average weight of the first 5 persons is 45 kg)
- (w5 + w6 + w7 + w8 + w9) / 5 = 55 (Average weight of the last 5 persons is 55 kg)
We can simplify these equations as follows -
- w1 + w2 + w3 + w4 + w5 + w6 + w7 + w8 + w9 = 450 (Multiplying both sides by 9)
- w1 + w2 + w3 + w4 + w5 = 225 (Multiplying both sides by 5)
- w5 + w6 + w7 + w8 + w9 = 275 (Multiplying both sides by 5)
Subtracting equation 2 from equation 1, we get -
- w6 + w7 + w8 + w9 = 225 (Subtracting both sides by w1 + w2 + w3 + w4 + w5)
Subtracting equation 3 from equation 1, we get -
- w1 + w2 + w3 + w4 = 175 (Subtracting both sides by w5 + w6 + w7 + w8 + w9)
Now, we need to find the weight of the 5th person, which is w5.
Adding equations 2 and 3, we get -
- w5 + w6 + w7 + w8 + w9 + w1 + w2 + w3 + w4 = 500 (Adding both sides)
Substituting the values we have found earlier, we get -
- w5 + 275 + 225 = 500 (Substituting w5 + w6 + w7 + w8 + w9 = 275 and w1 + w2 + w3 + w4 = 175)
Simplifying, we get -
- w5 = 50
Therefore, the weight of the 5th person is 50 kg, which is option C.
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