Question 36132
Find the difference between the two numbers and divide by 4 (which is 1 more than 3):

{{{(-10-18)/4= -28/4 = -7}}}


This is the common dfference between consecutive terms.  Now, start with 18 and add -7 consecutively (that is subtract 7) 


Start with 18
18-7= 11
11-7=4
4-7=-3
-3-7=-10


Therefore the three arithmetic means between 18 and - 10 would be 11, 4, and -3. 


R^2 at SCC
-3-7= -10