`A = (1 + 2/3 - 1/4) xx (0,8 - 3/40)^2 xx 17/240`
` = (12/12 + 8/12 - 3/12) xx (8/10 - 3/40)^2 xx 17/240`
` = ((12+8-3)/12) xx (32/40 - 3/40)^2 xx 17/240`
`= 17/12 xx (29/40)^2 xx 17/240`
` = 17/12 xx (29^2)/(40^2) xx 17/240`
` = 17/12 xx 841/1600 xx 17/240`
` = 14297/19200 xx 17/240`
` = 243049/4608000`
Vậy ` A= 243049/4608000`