Question 1120850
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I don't know what a "dot diagram" is; and drawing in typed messages doesn't work very well....<br>
There are 4 choices for the bill from envelope #1 and 5 choice for the bill from envelope #2.  The sample space contains 4*5 = 20 elements.<br>
There is no mathematical magic for counting the number of elements in the sample space that satisfy the requirement that the sum is more than 6.  Simply list the elements of the sample space (or look at your dot diagram?).<br>
1+2, 1+2, 1+5, 1+5, 1+10;
2+2, 2+2, 2+5, 2+5, 2+10;
2+2, 2+2, 2+5, 2+5, 2+10;
5+2, 5+2, 5+5, 5+5, 5+10<br>
How many of those sums are more than 6?