Huh? Where the hell are ya gettin 8x9??????????? Isn't 8x5 40? So wouldn't it be 4025? Which don't work at all! WTF?
15
2 = 225
15 is 1/2 way between 10 and 20
10X20=200 add the 25 = 225
25
2=625
25 is 1/2 way between 20 and 30
20X30 =600 add the 25 =625
See the pattern, now? It's hard to explain this way. 90X100= 9000 , 9000+25=95
2=9025