Question

tính nhanh

1+ 2 + 3 + ....... + 199 + 200

Answer 1

1+ 2 + 3 + ....... + 199 + 200

= ( 200 + 1 ) x [ ( 200 - 1 ) : 1 + 1 ] : 2 

= 201 x 200 : 2

= 20100

Answer 2

1 + 2 + 3 + ... + 199 + 200

= ( 1 + 200 ) + ( 2 + 199 ) + ... 

= 201 + 201 + 201 + 201 + ...

= 201 x 100

= 20100