`f, 417 + 235 + 583 + 765`
`= (417 + 583) + (235 + 765)`
`= 1000 + 1000`
`= 2000`
______________________
`n, 5 + 8 + 11 + 14 + ...+ 38 + 41`
`= (41 - 5) : 3 + 1` $\text{(Tìm số số hạng)}$
`= 13`
`= [(41 + 5) xx 13] : 2` $\text{(Tổng dãy số)}$
`= 299`
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`v, 49 - 51 + 53 - 55 + 57 - 59 + 61 - 63 + 65`
`= (49 - 51) + (53 - 55) + (57 -59) + (61 - 63) + 65`
`= (-2) + (-2) + (-2) + (-2) + 65`
`= (-2) . 4 + 65`
`= -8 + 65`
`= 57`
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`g, 67 + 135 + 33`
`= (67 + 33) + 135`
`= 100 + 135`
`= 235`
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`k, 277 + 113 + 323 + 87`
`= (277 + 323) + (113 + 87)`
`= 600 + 200`
`= 800`
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`m, 8 xx 17 xx 125`
`= (8 xx 125) xx 17`
`= 1000 xx 17`
`= 17000`