Hi Damien,
I didn't have the question so I took the long route but basically if you use CPI with more decimal places the answer works out. As you noticed rounding the CPI up even one decimal place makes a fairly large difference in the final answer.
You mentioned CPI = 240,000 / 253.700 so that tells me the question gives you the EV as 240,000 and AC as 253,700
You mentioned EAC = 700,000 / CPI which tells me that the question gives you BAC as 700,000
(I now know I didn't need to do that

)
CPI = 240,000 / 253,700 = 0.945945945
EAC = BAC / CPI => 700,000 / 0.945945945 => 740,000.00074
ETC = EAC - AC => 740,000.00074 - 253,700 => 486,300.00074 => 486,300