急!急!急! 超難數學題(8)

1. 先假設 rate 係 A%,
2500 x A% x 5 = 3000
A% = 0.24
A = 24%.

2. 先假設年期係 A,
10000 x 10% x A = 10000x2
10000 x 10% x A = 20000
10% x A = 2
A = 2 / 10%
A = 20.

1. $3000-$2500=$500
$500/5年=$100/1年interest
interest rate = $100/$2500*100
= 4% pa

式 : ($2500*5yrs*r%)+$2500=$3000
$2500*5*r%=$500
r%=$500/$12500
r%=0.04
r=4%

2. $10000既2倍= $20000. 即佢取回時要有$20000
那先將 $10000*10% = $1000 每年
$1000*10 = $10000
+回之前既資本. 佢可以取回$20000
Let Z be the time required
式 : $10000+($10000*10%*Zyrs) = $20000
$10000*10%*Zyrs = $20000-$10000
10%Zyrs =$10000/$10000
Zyrs = 1/10%
Zyrs =10yrs

3000=2500*(1+the interest rate p.a.*5)
3000/2500=1+the interest rate p.a.*5
1.2-1=the interest rate p.a.*5
0.2/5=the interest rate p.a.
the interest rate p.a.=0.04
the interest rate p.a.=4%

10000*2=10000*(1+10%*time)
20000/10000=1+10%*time
2-1=10%*time
1=0.1*time
1/0.1=time
time=10

2006-12-02 11:46:41 補充：
Time is 10years.

2006-12-02 11:49:30 補充：
人地個d答案冇個岩,請相信我

Actually, the bank calculates interest rate in COMPOUND INTEREST RATE, NOT SIMPLE INTEREST RATE.

Formula: Principal * Interest Rate (%) * Time = Interest

(1). For simple interest rate ONLY,

Interest for 5 years = 3,000 - 2,500
= 500

Let r be the interest rate,

2500 * r % * 5 = 500
12500 r % = 500
r % = 500 / 12500
r % = 0.04
r = (0.04 * 100) %
r = 4%

(2). Interest = Principal * 2
= 10000 * 2
= 20000

Let t be the time,
10000 * 10% * t = 20000
10% * t = 2
0.1t = 2
t = 20 years

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