由 Raceleader 於 星期日 八月 14, 2005 5:01 pm
依題意,總價x^2=10(2n+1)+k,n是非負整數,k=0,1,2,..,9
我們也可留意(10n+6)^2=100n^2+10(12n+3)+6及(10n+4)^2=100n^2+10(8n+1)+6
(10n+1)^2=100n^2+20n+1,不合題要,(10n-1)^2=100n^2-20n+1,不合題要
(10n+2)^2=100n^2+40n+4,不合題要,(10n-2)^2=100n^2-40n+4,不合題要
(10n+3)^2=100n^2+60n+9,不合題要,(10n-3)^2=100n^2-60n+9,不合題要
(10n+5)^2=100n^2+20(5n+1)+5,不合題要
因此尾數必為6,甲多給乙2元
Calculation Mathematics - 計算數學