Toán Lớp 6: tính nhanh:
10 + 11 + 12 + 13 + … + 99
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Toán Lớp 6: tính nhanh:
10 + 11 + 12 + 13 + … + 99
Comments ( 2 )
= ( 99 + 10 ) . [ ( 99 – 10 ) + 1 ] : 2
= 109 . 90 : 2
= 109 . 45
= 4905