如果某數先增加４０％，然後減少ａ％，則原數的整體百分數增減是+12%, 求a.
請列式計算!!!!!!!!
一條數!!!!
2007-09-24 12:57 am
回答 (4)
2007-09-24 1:15 am
✔ 最佳答案
設某數 = xx(1+40%)(1-a%)=x(1+12%)
=> 1.4(1-a%)=1.12
=> 1-a%=0.8
=> a=20
2007-09-24 1:23 am
let y be 某數.
original value:
y
new value:
(1+40%)y(1-a%)
% change:
{ [ (1+40%)y(1-a%) - y ] / y } *100% = 12%
{ [ y (1.4)*(1-a%) -1] / y }*100% = 12%
(1.4 - 1.4a% -1)*100% = 12%
(0.4 - 1.a% ) * 100% = 12%
0.4(1-3.5a%) *100% = 12%
1 -3.5a% = 0.3
-3.5a% = -0.7
a% = 0.2
a = 0.2 * 100
a = 20
original value:
y
new value:
(1+40%)y(1-a%)
% change:
{ [ (1+40%)y(1-a%) - y ] / y } *100% = 12%
{ [ y (1.4)*(1-a%) -1] / y }*100% = 12%
(1.4 - 1.4a% -1)*100% = 12%
(0.4 - 1.a% ) * 100% = 12%
0.4(1-3.5a%) *100% = 12%
1 -3.5a% = 0.3
-3.5a% = -0.7
a% = 0.2
a = 0.2 * 100
a = 20
2007-09-24 1:15 am
先列式:
(1+40%)(1-a%) = (1+12%)
1-a% = 1.12/1.4
1-a% = 0.8
-a% = 0.8-1
-a% = -0.2
a% = 0.2
a = 20%
希望幫到你.
(1+40%)(1-a%) = (1+12%)
1-a% = 1.12/1.4
1-a% = 0.8
-a% = 0.8-1
-a% = -0.2
a% = 0.2
a = 20%
希望幫到你.
參考: myself
收錄日期: 2021-04-24 00:15:49
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20070923000051KK03391