thanks for your answers guys !! 
However i have a 2nd question : 
I will take an example to illustrate my problem :
 A man have 30 kilos for his 15 reps max and 34 kilos for his 10 reps max on barbell curl.
If he want an increment , he will do for his 6 workouts on 15s block : 20 , 22 , 24 , 26, 28 and 30.
for his 10s two week block : he will do 24 , 26 , 28 , 30 , 32 , 34.
28 kilos represents nearly 82 % of his 15 reps max but the same weight represents 93 % of his 10 Reps max.
My question is ( finally 
		
		
	
	
 ) : Is there any problem when we lift the same weight on 15 and 10 or even 5 ? or it is totally normal ?
thanks for your answers !! 
 
 -NoMercy-