Question 1074129
<pre>
Since there are only 10 terms, it's just as easy not to
use formulas, especially since we're going to have to
calculate all the terms:

Start with a5 = 24, subtract d each time for the 
terms before the 5th and add d each time for the
terms after 5th:


 a1 = 24-4d, 
 a2 = 24-3d, 
 a3 = 24-2d, 
 a4 = 24-d, 
 a5 = 24, 
 a6 = 24+d,
 a7 = 24+2d, 
 a8 = 24+3d,
 a9 = 24+4d, 
a10 = 24+5d 

a7 - a10 = (24+2d) - (24+5d) = 15
                 24+2d-24-5d = 15
                         -3d = 15
                           d = -5
                          

 a1 = 24-4d = 24-4(-5) = 24+20 = 44 
 a2 = 44+(-5) = 39 
 a3 = 39+(-5) = 34  
 a4 = 34+(-5) = 29 
 a5 = 24           <-- given, which checks, since 24=29+(-5) 
 a6 = 24+(-5) = 19
 a7 = 19+(-5) = 14 
 a8 = 14+(-5) = 9
 a9 =  9+(-5) = 4  
a10 =  9+(-5) = -1

Checking: a7 - a10 = 14-(-1) = 14+1 = 15

Edwin</pre>