Shortcut Trick
Let the three numbers in ascending order be x, y, and z.
Sum of numbers = 38 × 3 = 114.
Given: y = (x + z) − 20 ⇒ x + z = y + 20.
Substitute in sum: (y + 20) + y = 114 ⇒ 2y = 94 ⇒ y = 47.
Now, x + z = 67 and z − x = 31 (Range). Adding both gives 2z = 98 ⇒ z = 49.
∴ The correct answer is 49.
Alternate Method
Given:
Mean of three numbers = 38
Range of data = 31
Middle number = Sum of other two − 20
Formula Used:
Mean = Sum of observations ÷ Number of observations
Range = Largest value − Smallest value
Calculations:
Let the three numbers in ascending order be x, y, and z.
⇒ Mean = (x + y + z) ÷ 3 = 38
⇒ x + y + z = 114 --- (Equation 1)
The range of the data is 31:
⇒ z − x = 31 --- (Equation 2)
The middle number (y) is 20 less than the sum of the other two numbers (x + z):
⇒ y = (x + z) − 20
⇒ x + z = y + 20 --- (Equation 3)
Substitute Equation 3 into Equation 1:
⇒ (y + 20) + y = 114
⇒ 2y + 20 = 114
⇒ 2y = 94
⇒ y = 47
Substitute y = 47 into Equation 1:
⇒ x + 47 + z = 114
⇒ x + z = 67 --- (Equation 4)
Now, solve Equation 2 and Equation 4 simultaneously:
⇒ z − x = 31
⇒ z + x = 67
Adding both equations:
⇒ 2z = 98
⇒ z = 49
Subtracting Equation 2 from Equation 4:
⇒ 2x = 36
⇒ x = 18
Thus, the three numbers are 18, 47, and 49.
The largest number is 49.
Verification of Options:
• Option 1 (47): If the largest number is 47, then the smallest is 47 − 31 = 16. The middle number would be 114 − 47 − 16 = 51, which is greater than the largest number (contradiction).
• Option 2 (49): If the largest number is 49, then the smallest is 49 − 31 = 18. The middle number is 114 − 49 − 18 = 47. This satisfies all conditions perfectly.
• Option 3 (51): If the largest number is 51, then the smallest is 51 − 31 = 20. The middle number would be 114 − 51 − 20 = 43. But 43 is not equal to (20 + 51) − 20 = 51 (contradiction).
• Option 4 (45): If the largest number is 45, then the smallest is 45 − 31 = 14. The middle number would be 114 − 45 − 14 = 55, which is greater than the largest number (contradiction).
∴ The correct answer is 49.
Additional Information
Mean (Average)
The sum of all values divided by the total number of values. Formula: Mean = (Σx) ÷ n.
Range
The difference between the highest (largest) and lowest (smallest) values in a data set. Formula: Range = Maximum − Minimum.
Median of Three Numbers
When three numbers are arranged in ascending order, the middle number is the median.