1. The average of five consecutive odd numbers is 51. What is the difference between the highest and lowest number?
Answer: Option C
Explanation:
Let the numbers be x, x + 2, x + 4, x + 6 and x + 8.
Then, [latex]\frac{x + (x + 2) + (x + 4) + (x + 6) + (x + 8) }{5}[/latex] = 51
5x + 20 = 255
x = 47
So, required difference = (47 + 8) – 47 = 8
2. Find the average of first 30 natural numbers.
A. 12
B. 15.5
C. 14.5
D. 16
Answer: Option B
Explanation:
Sum of first n natural numbers = [latex]\frac{n(n+1) }{2}[/latex]
Hence, sum of first 30 natural numbers = [latex]\frac{30 × 31 }{2}[/latex] = 465
Therefore, required average of = [latex]\frac{465 }{30}[/latex] = 15.5
3. The average weight of three boys P, Q and R is 54 kg, while the average weight of three boys Q, S and T is 60 kg. What is the average weight of P, Q, R, S and T?
A. 66.4 kg
B. 63.2 kg
C. 58.8 kg
D. Data Inadequate
Answer: Option D
Explanation:
Total weight of (P + Q + R) = {54*3} kg = 162 kg
Total weight of(Q + S + T) = (60 *3) kg = 180 kg
Adding both, we get : P + 2Q + S + R + T = (162 + 180) kg = 342 kg
So, to find the average weight of P, Q, R, S & T, we ought to know Q's weight, which is not given.
The data is inadequate.
4. If the sum of three consecutive even numbers is 44 more than the average of these numbers, then the largest of these numbers is?
A. 20
B. 24
C. 22
D. None of these
Answer: Option B
Explanation:
Let the smallest of these number be x. The other two numbers are (x + 2) and (x + 4).
x + (x + 2) + (x + 4) = [latex]\frac{(X + (X+2) + (x+4)) }{3}[/latex] + 44
3x + 3*(x + 2) + 3*(x + 4) = x + (x + 2) + (x + 4) + 132
9x + 18 = 3x + 138
6x = 120
x = 20
Therefore, the largest number is 24.
5. If from a group of 5 people, an old member is replaced by a new one, the average age is same as it was 3 years ago. What is the difference between the ages of the old member and the new one?
Answer: Option B
Explanation:
The present average age is (x + 3) when the old member is present and it equals to x when an old member is replaced by a new one.
The difference in the ages of the old member and the new one is equal to the difference in the total age before and after the replacement = 15 years.