年限平均法每年折舊=5000000*（1-2%）/20=245000

雙倍余額遞減法 第一年5000000*2/20=500000 第二年=（5000000-500000）*2/5=450000 第三年=(5000000-500000-450000)*2/20=405000 第四年=（5000000-500000-450000-405000）*2/20=364500 第五年=(5000000-500000-450000-405000-364500)*2/20=328050 第六年=(5000000-500000-450000-405000-364500-328050）*2/20=295245 第七年=(5000000-500000-450000-405000-364500-328050-295245)*2/20=265720.5 第八年=(5000000-500000-450000-405000-364500-328050-295245-265720.5）*2/20=239148.45 第九年=(5000000-500000-450000-405000-364500-328050-295245-265720.5-239148.45)*2/20=215233.605

第十年=(5000000-500000-450000-405000-364500-328050-295245-265720.5-239148.45-215233.605）*2/20=193710.24 第十一年=(5000000-500000-450000-405000-364500-328050-295245-265720.5-239148.45-215233.605-193710.24)*2/10=174339.216 第十二年=(5000000-500000-450000-405000-364500-328050-295245-265720.5-239148.45-215233.605-193710.24-174339.216)*2/10=156905.2944 第十三年=(5000000-500000-450000-405000-364500-328050-295245-265720.5-239148.45-215233.605-193710.24-174339.216-156905.2944)*2/10=141214.76496 第十四年=(5000000-500000-450000-405000-364500-328050-295245-265720.5-239148.45-215233.605-193710.24-174339.216-156905.2944)*2/10=1270932.88464 第十五年=(5000000-500000-450000-405000-364500-328050-295245-265720.5-239148.45-215233.605-193710.24-174339.216-156905.2944-1270932.88464)*2/10=1143839.59618 第十六年(5000000-500000-450000-405000-364500-328050-295245-265720.5-239148.45-215233.605-193710.24-174339.216-156905.2944-1270932.88464-1143839.59618)*2/10=1029455.63657 第十七年=(5000000-500000-450000-405000-364500-328050-295245-265720.5-239148.45-215233.605-193710.24-174339.216-156905.2944-1270932.88464-1143839.59618-1029455.63657)*2/10=926510.07292 第十八年=(5000000-500000-450000-405000-364500-328050-295245-265720.5-239148.45-215233.605-193710.24-174339.216-156905.2944-1270932.88464-1143839.59618-1029455.63657-926510.07292)*2/10=833859.065625 第十九年 第二十年 （原值-上面十八年累計折舊-凈殘值）/2