The mean of four numbers is 18 . H one of the four numbers is removed, the mean of the three remaining numbers is 17 . What is the value of the number that was removed?

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To solve the problem, we can follow these steps:

1. **Extract known conditions:**
   - The mean of four numbers is 18.
   - When one number is removed, the mean of the remaining three numbers is 17.

2. **Calculate the total of the four numbers:**
   The mean of four numbers is given by the formula:
   $$
   \text{Mean} = \frac{\text{Total}}{\text{Count}}
   $$
   Therefore, we can express the total of the four numbers $$ T_4 $$ as:
   $$
   T_4 = \text{Mean} \times \text{Count} = 18 \times 4 = 72
   $$

3. **Calculate the total of the three remaining numbers:**
   When one number is removed, the mean of the three remaining numbers is 17. Thus, the total of the three numbers $$ T_3 $$ can be calculated as:
   $$
   T_3 = \text{Mean} \times \text{Count} = 17 \times 3 = 51
   $$

4. **Determine the value of the removed number:**
   Let $$ x $$ be the number that was removed. The relationship between the totals can be expressed as:
   $$
   T_4 = T_3 + x
   $$
   Substituting the known values:
   $$
   72 = 51 + x
   $$
   To find $$ x $$, we can rearrange the equation:
   $$
   x = 72 - 51 = 21
   $$

Thus, the value of the number that was removed is $$ \boxed{21} $$.
The number removed is 21.

The mean of four numbers is 18 . H one of the four numbers is removed, the mean of the three remaining numbers is 17 . What is the value of the number that was removed?

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