1. The price of a toy car was increased by 20% and then decreased by $30. If the price now is marked as $162, find the overall % change of the price.
2. At the end of 2004, Sam's monthly salary is $10000. His monthly salary was increased by R% at the end of 2005 and then decreased by R% at the end of 2006. If his monthly salary at the end of 2006 is $9500, find the value of R.
thx!
[20 marks] F.3 Maths
2007-12-31 6:17 pm
回答 (3)
2007-12-31 6:51 pm
let the price of the toy car be y,
y(1+20%) -30=162
y(1+20%)=162+30
y=192/(1+20%)
y=160
decreased %: 30/160 x100%
=18.75%
so the overall % change of the price:(1+20%-18.75% -1)x100%
=(1.0125-1)
=0.0125x100%
=+1.25%
2007-12-31 11:03:28 補充：
2. 10000(1 R%)(1-R%)=9500 10000 10000R%(1-R%)=9500 [(10000 10000R%)-R%(10000 R%)]=9500 (10000-R^2%)=9500 10000-9500=R^2% 500=R^2% 500/100%=R^2 5=R^2 R=開方5
2007-12-31 19:39:46 補充：
sorry 錯左d野2. 10000(1 R%)(1-R%)=950010000 10000R%(1-R%)=9500[(10000 10000R%)-R%(10000 R%)]=9500(10000-R%^2)=950010000-9500=R%^2500=(R%)^2500開方=R%500開方/100=RR=0.2236(corr. to 4 sig.fig)
y(1+20%) -30=162
y(1+20%)=162+30
y=192/(1+20%)
y=160
decreased %: 30/160 x100%
=18.75%
so the overall % change of the price:(1+20%-18.75% -1)x100%
=(1.0125-1)
=0.0125x100%
=+1.25%
2007-12-31 11:03:28 補充：
2. 10000(1 R%)(1-R%)=9500 10000 10000R%(1-R%)=9500 [(10000 10000R%)-R%(10000 R%)]=9500 (10000-R^2%)=9500 10000-9500=R^2% 500=R^2% 500/100%=R^2 5=R^2 R=開方5
2007-12-31 19:39:46 補充：
sorry 錯左d野2. 10000(1 R%)(1-R%)=950010000 10000R%(1-R%)=9500[(10000 10000R%)-R%(10000 R%)]=9500(10000-R%^2)=950010000-9500=R%^2500=(R%)^2500開方=R%500開方/100=RR=0.2236(corr. to 4 sig.fig)
參考: 在下
2007-12-31 6:48 pm
1: 1.25%
p.s. (162-162+30除以120%)除以162+30除以120%=1.25%
2. 22.33............(22三分一)
p.s. 500=10000times(100-r%)times(100+r%)
p.s. (162-162+30除以120%)除以162+30除以120%=1.25%
2. 22.33............(22三分一)
p.s. 500=10000times(100-r%)times(100+r%)
參考: me
2007-12-31 6:44 pm
等我一陣,宜家計
2007-12-31 10:45:48 補充：
咦？有人計o左，咁我唔計la
2007-12-31 10:45:48 補充：
咦？有人計o左，咁我唔計la
收錄日期: 2021-04-25 19:56:22
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20071231000051KK00772