以下既題目我都唔識點做..
請提供步驟:
1)If a is 15%hreater than B and B is 8% greater than C, then C is how many percent of A?
Ans=80.5%
2)IF the length of a rectangle is decreased by 20% and the width of it it increased by 20% find the %change of its area.
Ans= - 4%
3)A number is increased by m% and then decreased by n%. If the number obtained become doubled find m in terms of n .
Ans= m=100(100+n) over 100-n
4)$20000 is invested for 4 years at 10% p.a compounded half yearly.Find the compound interest
Ans$9549
5)Find the difference between the somple interest and the compounded intersest payable monthly on $10000 ai 6% p.a for 2years
Ans=72
6)The population of a town is 5000. 5years later its population is 6691. Assuming the growth rate is constant throughout the years find the annual growth rate
Ans=6%
7)40 cm^3 of a certain solution contains alcohol and water in the ratio 3:1.How much water must be added to hte solution such that the new ratio of alcohol to water is 2:1
Ans=5cm^3
8)The height of two similar cones are in the ratio 4:5 find the ratio of their volume
Ans=64:125
初中maths 求救 答得幾多就幾多
2011-09-03 9:31 pm
回答 (3)
2011-09-03 11:45 pm
✔ 最佳答案
1)a=b(1+15%)b=c(1+8%)
a=c(1+8%)(1+15%)
a=c*(27/25)*(23/20)
a=c*(621/500)
c=a*(500/621)
c=a*80.5%
2)let a and b be the length and width of the rectangle respectively
original area=ab
new area=a(1-20%)*b(1+20%)
=ab(1-20%)(1+20%)
=ab*(4/5)*(6/5)
=(24/25)ab
%change=(24/25ab-ab)/ab*100%
=(-1/25)*100%
=-4%
3)let x be the number.
x(1+m%)(1-n%)=2x
(1+m%)(1-n%)=2
((100+m)/100)*((100-n)/100)=2
(100+m)(100-n)=20000
10000+100m-100n-mn=20000
m(100-n)=10000+100n
m=(10000+100n)/(100-n)
m=100(100+n)/(100-n)
4.amount=20000*(1+10%/2)^8
=20000*1.05^8
=$29549
compound interest=29549-20000=$9549
5.simple interest=10000*6%*2=$1200
amount=10000*(1+6%/12)^24
=10000*(1+0.5%)^24
=$11272
compound interest=11272-10000=$1272
difference=1272-1200=$72
6.let r be the annual growth rate
5000(1+r)^5=6691
r=開5次方(6691/5000)-1
r=0.06=6%
annual growth rate=6%
7.amount of alchol=40*(3/3+1)=30cm^3
amount of water=40-30=10cm^3
let x be the amount of water added to the solution
30:10+x=2:1
30/(10+x)=2
x=5
amount of water added to the solution=5cm^3
8.ratio of their volume=(4/5)^3
=64/125
=64:125
參考: my answer
2011-09-03 11:59 pm
1) a=Ｂ(1+15%)
a/1.15=Ｂ
Ｂ=Ｃ(1+8%)
Ｂ=Ｃ(1.08)
a/1.15=1.08Ｃ
0.805a=Ｃ(corr. to 3sig fig)
Ｃ=80.5%a (corr to 3 sig fig)
2) let the length be l and the width be w.
[l(1-20%)w(1+20%)-lw]/lwＸ100%
=-0.04lw/lwＸ100%
=-4%
3) let the original number be a.
a(1+m%)(1-n%)=2a
a[(100+m)/100][(100-n)/100]=2a
(10000+100m-100n-mn)/10000=2
10000+100m-100n-mn=20000
100m-100n-mn=10000
100m-mn=10000+100n
m(100-n)=10000+100n
m=(10000+100n)/(100-n)
4) 20000(1+10%/2)^(4*2)-20000
=20000*1.05^8-20000
=$9549 (corr to nearest dollar)
5) Ｓimple interest=10000(6(2)/100)
=$1200
Ｃompound interest=10000(1+6%/12)^(12*2)-10000
=$1271 (corr to nearest dollar)
Ｄifference=1271-1200
=$71(correct to nearest dollar)
6) let the annual growth rate be x%
5000(1+x)^5=6691
(1+x)^5=1.3382
x=6%(corr to nearest integer)
7) amount of alcohol=40[3/(3+1)]
=30cm cube
let the amount of water added be xcm cube
30/(40-30+x)=2/1
30/(10+x)=2
15=10+x
x=5
therefore, 5cm cube of water should be added.
8) ratio of their volume=(4/5)^3
=64:125
a/1.15=Ｂ
Ｂ=Ｃ(1+8%)
Ｂ=Ｃ(1.08)
a/1.15=1.08Ｃ
0.805a=Ｃ(corr. to 3sig fig)
Ｃ=80.5%a (corr to 3 sig fig)
2) let the length be l and the width be w.
[l(1-20%)w(1+20%)-lw]/lwＸ100%
=-0.04lw/lwＸ100%
=-4%
3) let the original number be a.
a(1+m%)(1-n%)=2a
a[(100+m)/100][(100-n)/100]=2a
(10000+100m-100n-mn)/10000=2
10000+100m-100n-mn=20000
100m-100n-mn=10000
100m-mn=10000+100n
m(100-n)=10000+100n
m=(10000+100n)/(100-n)
4) 20000(1+10%/2)^(4*2)-20000
=20000*1.05^8-20000
=$9549 (corr to nearest dollar)
5) Ｓimple interest=10000(6(2)/100)
=$1200
Ｃompound interest=10000(1+6%/12)^(12*2)-10000
=$1271 (corr to nearest dollar)
Ｄifference=1271-1200
=$71(correct to nearest dollar)
6) let the annual growth rate be x%
5000(1+x)^5=6691
(1+x)^5=1.3382
x=6%(corr to nearest integer)
7) amount of alcohol=40[3/(3+1)]
=30cm cube
let the amount of water added be xcm cube
30/(40-30+x)=2/1
30/(10+x)=2
15=10+x
x=5
therefore, 5cm cube of water should be added.
8) ratio of their volume=(4/5)^3
=64:125
2011-09-03 11:06 pm
If a is 15%greater than B and B is 8% greater than C, then C is how many percent of A?
a=1.15b
b=c(1+8%)
c=b/1.08
________________
c/a=(b/1.08)/b=80.5%(cor. to 3 sig. figs.)
a=1.15b
b=c(1+8%)
c=b/1.08
________________
c/a=(b/1.08)/b=80.5%(cor. to 3 sig. figs.)
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