`0.8xx?=0.0004`

Options

A. 0.0005
B. 0.005
C. 0.5
D. 5.0E-5

Answer

To solve the equation \(0.8 \times ? = 0.0004\), we need to find the value of the question mark. Let's go through the steps systematically.

### Step 1: Set up the equation
We start with the equation:
\[ 0.8 \times ? = 0.0004 \]

### Step 2: Isolate the question mark
To find the value of the question mark, we need to isolate it. We can do this by dividing both sides of the equation by \(0.8\):
\[ ? = \frac{0.0004}{0.8} \]

### Step 3: Simplify the division
Now, we will perform the division. To make it easier, we can remove the decimal points. We can multiply the numerator and denominator by \(10\) to convert \(0.0004\) and \(0.8\) into whole numbers:
\[ ? = \frac{0.0004 \times 10}{0.8 \times 10} = \frac{0.004}{8} \]

### Step 4: Perform the division
Now we divide \(0.004\) by \(8\):
\[ ? = 0.004 \div 8 \]

To perform this division, we can convert \(0.004\) into a fraction:
\[ 0.004 = \frac{4}{1000} = \frac{1}{250} \]
Now, we divide:
\[ ? = \frac{1}{250} \div 8 = \frac{1}{250 \times 8} = \frac{1}{2000} \]

### Step 5: Convert back to decimal
Now, we convert \(\frac{1}{2000}\) back to decimal form:
\[ ? = 0.0005 \]

### Final Answer
Thus, the value of the question mark is:
\[ ? = 0.0005 \]