The ratio of the three numbers A, B and C is 4,5:2,3:1,2, and the number A is 18 greater than the number C, what is the average number of A and B?
甲、乙、丙三个数的比是4,5：2,3：1,2，甲数比丙数大18，则甲、乙的平均数是多少．
<gadget id="calculator">45 + 23 + 12</gadget>
<output>80</output>

<gadget id="calculator">45 / 80</gadget>
<output>9/16 = around 0.5625</output>

<gadget id="calculator">12 / 80</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">(9/16) - (3/20)</gadget>
<output>33/80 = around 0.4125</output>

<gadget id="calculator">18 / (33/80)</gadget>
<output>480/11 = around 43.636364</output>

<gadget id="calculator">(480/11) * (9/16)</gadget>
<output>270/11 = around 24.545455</output>

<gadget id="calculator">23 / 80</gadget>
<output>23/80 = around 0.2875</output>

<gadget id="calculator">(480/11) * (23/80)</gadget>
<output>138/11 = around 12.545455</output>

<gadget id="calculator">(270/11) + (138/11)</gadget>
<output>408/11 = around 37.090909</output>

<gadget id="calculator">(408/11) / 2</gadget>
<output>204/11 = around 18.545455</output>

<result>204/11 = around 18.545455</result>