1.The width of a rectangle is increased by 60% . If its area remains unchanged , find the percentage change in its length.
2.Jack's monthly working time is increased by 25% , but his wage per hour is decreased by 20% .Find the percentage change in Jack's monthly income.
maths..
2007-07-16 10:13 pm
回答 (2)
2007-07-16 10:24 pm
✔ 最佳答案
( 1 ) Let the length be x, the width be y and the percentage change be r%. x ( 1 + r% ) y ( 1 + 60% ) = xy
1.6 ( 1 + r% ) = 1
1 + r% = 5 / 8
r% = -3 / 8
r = - 37. 5%
( 2 ) Let the monthly working time be x h and the wage per hour be y.
New monthly income : x ( 1 + 25% ) y ( 1 - 20% )
= xy
So the percentage change : {( xy - x y ) / xy }( 100% ) = 0%
2007-07-16 16:02:17 補充：
The original monthly income is xy, sorry for missing that out.
參考: My Maths Knowledge
2007-07-16 10:38 pm
1) let the ratio of length change = A
the width of rectangle = W
the length of rectangle = L
W x L = 1.6W x AL
A = 1/1.6 = 0.625
therefore the percentage change = (1 - 0.625) x 100% = 37.5% (decreased)
2) let the original monthly working time = T
the original wage per hour = M
after change income per monthly
= 1.25T x 0.8M
= T x M
therefore is no change of monthly income.
the width of rectangle = W
the length of rectangle = L
W x L = 1.6W x AL
A = 1/1.6 = 0.625
therefore the percentage change = (1 - 0.625) x 100% = 37.5% (decreased)
2) let the original monthly working time = T
the original wage per hour = M
after change income per monthly
= 1.25T x 0.8M
= T x M
therefore is no change of monthly income.
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