Let \( x \) be the number of ounces of the 7.9% ground cinnamon substance that the physician used. Thus, the other substance (3.7% ground cinnamon) must have been \( 1 - x \) ounces, since the total amount mixed is 1 ounce.
We can set up the equation based on the amount of ground cinnamon in each substance:
-
The amount of ground cinnamon in the 3.7% substance is: \[ 0.037(1 - x) \]
-
The amount of ground cinnamon in the 7.9% substance is: \[ 0.079x \]
-
The total amount of ground cinnamon in the mixture is equal to the amount of ground cinnamon in the resulting mixture (which is 6.5% of 1 ounce): \[ 0.065 \cdot 1 = 0.065 \]
Now we can set up the equation: \[ 0.037(1 - x) + 0.079x = 0.065 \]
Expanding the left side of the equation: \[ 0.037 - 0.037x + 0.079x = 0.065 \]
Combining like terms, we have: \[ 0.037 + 0.042x = 0.065 \]
Next, subtract \( 0.037 \) from both sides: \[ 0.042x = 0.065 - 0.037 \] \[ 0.042x = 0.028 \]
Now, solve for \( x \): \[ x = \frac{0.028}{0.042} = \frac{28}{42} = \frac{2}{3} \]
Thus, the physician used \( \frac{2}{3} \) ounces of the 7.9% substance. To find the answer in decimal form: \[ \frac{2}{3} \approx 0.6667 \]
Therefore, the answer is: \[ \boxed{\frac{2}{3}} \text{ ounces of the 7.9% substance} \]