For this, I would turn your mixed number into an improper fraction. 
whole•denominator+numerator over the denominator 
1(4)=4+1=5. So 5/4. 
Now we want to cut it in half so we're going to multiply by a half: 5/4 x 1/2=5/8
The equation would be: 1&1/4 (5/4) divided by x amount of flour equals 1/2. 
OR 
(5/4)/x=1/2