(a+1)+(a+2)+(a+3)+(a+4)+(a+5)=65
a+1+a+2+a+3+a+4+a+5=65
5a+15=65
5a=50
a=10
(a + 1) + ( a + 2) + (a + 3) + (a + 4) + (a + 5) = 65
a + 1 + a + 2 + a + 3 + a + 4 + a + 5 = 65
(a + a + a + a + a) + (1+ 2+3+4+5) = 65
5a + 15 = 65
5a = 65 - 15 = 50
a = 50 : 5 = 10