Question

if the average of three numbers is 25. two of these numbers are 18 and 40, what is the third number? 20 17 15 30

Explanation:

Step1: Recall the average formula

The formula for the average of \( n \) numbers is \( \text{Average} = \frac{\text{Sum of numbers}}{n} \). Here, \( n = 3 \) and the average is 25, so the sum of the three numbers is \( 25\times3 = 75 \).

Step2: Let the third number be \( x \)

We know two numbers are 18 and 40. So, \( 18 + 40 + x = 75 \).

Step3: Solve for \( x \)

First, calculate \( 18 + 40 = 58 \). Then, \( x = 75 - 58 = 17 \).

Answer:

17