What number must be added to the set {5, 15, 25} to make the average 20?
Category: Math · Difficulty: expert
Hint: Calculate the total needed for the average.
Answer
25
Explanation
The average is (5 + 15 + 25 + x)/4 = 20. Thus, 45 + x = 80, so x = 35.
This is a expert math riddle — one of the harder riddles here. The answer is 25.
More Math riddles
- I am a trio of numbers, with a difference of one among them. Their sum equals nine. What am I?
- I am increased by halving my value and multiplied by doubling. What am I?
- I can express equality, I can relate comparisons, but I am not a thing. What am I?
- I can represent much more than I appear, yet I rely on a base to define my worth. What am I?
- I can loop and twist but remain in place, drawing paths with each change. What am I?
- I can predict but never know, I follow steps yet have no feet. What am I?
- I hold values but can't be touched, I link ideas yet have no voice. What am I?
- I have no edges yet can enclose, I can measure but never touch. What am I?