a)
2005 - 754 + 107 - 238 = 1 120
= 1 251 + 107 - 238 =
= 1358 - 238 =
= 1 120
______________________
b)
1 + 3 + 5 + ....... + 19 = 100
= ( 1 + 19 ) + ( 3 + 17 ) + ( 5 + 15 ) + ( 7 + 13 ) + ( 9 + 11 ) =
= 20 + 20 + 20 + 20 + 20 =
= 100
sau aplic formula sumei lui Gauss:
= [ ( 19 - 1 ) : 2 + 1 ] termeni × ( 1 + 19 ) : 2 =
= 10 × 20 : 2 =
= 200 : 2 =
= 100
