Question 1202222
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The problem can easily be worked informally by working backwards, using logical reasoning.<br>
The green robot washed half of the windows that were left when it started working. That means it left half of the windows unwashed.  Those are the 10 windows that the last robot washed.  So when the green robot started washing windows, the number left to be washed was 2(10) = 20.<br>
Similarly, the red robot washed half of all the windows, so the 20 windows it left unwashed were half of the total number of windows, making the total number of windows 2(20) = 40.<br>
ANSWER: 40<br>