Evaluation: a=2.5, b=-0.4, find the value of a+ab+b.
求值：a=2.5，b=-0.4，求a+ab+b的值．
<gadget id="calculator">2.5 * (-0.4)</gadget>
<output>-1</output>

<gadget id="calculator">2.5 + (-1) + (-0.4)</gadget>
<output>1.1</output>

<result>1.1</result>