Răspuns :
10 +20 +30 + .......+100
n = ( 100 - 10 ) : ( 20 - 10) +1
n = 90 : 10 +1
n = 9+1
n = 10
S= [( 100 +3 ) × 10 ] : 2
S= ( 103 × 10 ) : 2
S= 1030 : 2
S= 515.
n = ( 100 - 10 ) : ( 20 - 10) +1
n = 90 : 10 +1
n = 9+1
n = 10
S= [( 100 +3 ) × 10 ] : 2
S= ( 103 × 10 ) : 2
S= 1030 : 2
S= 515.