→ math365 : 感謝 04/02 12:43
※ 引述《math365 (math365)》之銘言:
: https://i.imgur.com/SZvSZPX.jpg
19.
x + y = 8 = na
x/3 + y/5 = a
=> (n/3)x + (n/5)y = 8 = x + y
=> [(n/3) - 1]x = [1 - (n/5)]y
=> n = 4
選(B)
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