4.1 #3,8,11,12,16,18,44,51,55 <br>
4.3 #3,11,22,29,39 <p>

4.1 #8. No initials repeated: 26 * 25 * 24.
<p>
4.1 #12. 2^6 + 2^5 + 2^4 + ... + 2^0. (Don't leave out the empty string,
it counts for one.)
<p>
4.1 #16. How many with x? 26^4 - 25^4.
<p>
4.1 #18. 
<menu>
<li> floor(1000/7)
<li> floor(1000/7) - floor(1000/77)
<li> floor(1000/77)
<li> floor(1000/7) + floor(1000/11) - floor(1000/77)
<li> floor(1000/7) - floor(1000/77) + floor(1000/11) - floor(1000/77)
<li> 1000 - (floor(1000/7) + floor(1000/11) - floor(1000/77))
<li> 10*9*8
<li> 5*9*8 (pick the 1s digit first, then the 10s, then the 100s)
</menu>

<p>
4.1 #44. 38 CS + 23 math - 7 joint = 54 in all
<p>

4.3 #22a. Pick 5 people, and remove the selections of all men: 
(7+9 choose 5) minus (9 choose 5).
<p>
b. Also remove the all women selections:
(7+9 choose 5) minus (9 choose 5) minus (7 choose 5).