Question 117449
<pre><font size = 5><b>
Let A be the set of all composites less than 10,
and B be the set of positive even integers less 
than 10. How many different sums of the form a + b 
are possible if a is in A and b is in B?

A = {4,6,8,9}
B = {2,4,6,8}

Make an addition table:

+ A  4   6   8   9
B  ———————————————
2 |  6   8  10  11
  |
4 |  8  10  12  13
  |
6 | 10  12  14  15
  |
8 | 12  14  16  17

The different sums are

6, 8, 10, 11, 12, 13, 14, 15, 16, 17

So there are 10 different sums.

Edwin</pre>