P is a point on the line segment AB, AP=(3/5)AB, M is the midpoint of AB, if PM=2, find the length of AB.
P为线段AB上一点，AP=(3/5)AB，M是AB的中点，若PM=2，求AB的长．
<gadget id="calculator">3 / 5</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(3/5) - (1/2)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">2 / (1/10)</gadget>
<output>20</output>

<result>20</result>