Four numbers 1, 2, 3, and 6 are written on four identical small balls, and each time two balls are randomly drawn out of them, and the two numbers above are added together, what is the probability that the sum is an even number? ．
四个同样的小球上，分别写有1、2、3、6四个数字，每次从中任意摸出两个球，并将上面的两个数字相加，和是偶数的可能性是多少．
<gadget id="calculator">2 / 6</gadget>
<output>1/3 = around 0.333333</output>

<result>1/3 = around 0.333333</result>