1.The sum of three numbers A,B and C is 405. Ais four times of B, and C is greater than A by 45. Find these three numbers.
2.In a school 330 students are boys, and they are 60% of the students .Find the total numberof student in the school.
3.The share price of a company is now $98.5. If the price increase by 12% every year,how many years later will the share price be over $300?
Maths
2007-06-10 9:01 pm
回答 (4)
2007-06-11 3:15 am
✔ 最佳答案
1.LET B BE XA=4X
C=4X+45
A+B+C=405
4X+X+4X+45=405
9X+45=405
X=40
A=4X
=4*40
=160
B=X=40
C=4X+45
=4*40+45
=205
2.330/60%=550
2007-06-14 1:30 am
這個「最佳回答」是發問者自選的，
但是，
第一，這個「最佳回答」只在發問者的三條問題當中，答了兩條......而其他答者，則全部答哂！
第二，這個「最佳回答」是比其餘兩個答者答問題的時間遲六粒鐘......
第三，這個「最佳回答」答到一舊舊咁，其餘兩個回答則清楚多了！
這個「最佳回答」不但比其餘兩個回答答得較為遜色，
而且，好話唔好聽，如果這條問題交付投票，都不知有沒有人會選佢......
但是，
第一，這個「最佳回答」只在發問者的三條問題當中，答了兩條......而其他答者，則全部答哂！
第二，這個「最佳回答」是比其餘兩個答者答問題的時間遲六粒鐘......
第三，這個「最佳回答」答到一舊舊咁，其餘兩個回答則清楚多了！
這個「最佳回答」不但比其餘兩個回答答得較為遜色，
而且，好話唔好聽，如果這條問題交付投票，都不知有沒有人會選佢......
2007-06-10 9:27 pm
A + B + C = 405 __________(1)
A = 4B _________________(2)
C - A = 45 ______________(3)
From (3), we have:
C = 45 + A
Sub (3) into (1) , we have:
A + B +C = 405
A + B + 45 + A = 405
2A + B = 360
Sub ( 2) into 2A + B = 360, we have:
2 ( 4B ) + B = 360
9B = 360
B = 40
Sub B = 40 into (1), we have:
A = 4 ( 40 )
A = 160
Sub A = 160 into ( 3 )
C - 160 = 45
C = 205
So, A = 160, B = 40, C = 205
2)
Let the total number of student be n
330 = n * ( 60 / 100)
n = 550
So there are 550 students in the school in total.
3)
98.5 * (112/100 ) ^ n > 300
(112/100 ) ^ n > 3000 / 985
(112/100 ) ^ n > 600 / 197
So 10 years later the share price will be over $300
2007-06-11 16:26:53 補充：
三題答得兩題，
仲要是最遲答的那個......
A = 4B _________________(2)
C - A = 45 ______________(3)
From (3), we have:
C = 45 + A
Sub (3) into (1) , we have:
A + B +C = 405
A + B + 45 + A = 405
2A + B = 360
Sub ( 2) into 2A + B = 360, we have:
2 ( 4B ) + B = 360
9B = 360
B = 40
Sub B = 40 into (1), we have:
A = 4 ( 40 )
A = 160
Sub A = 160 into ( 3 )
C - 160 = 45
C = 205
So, A = 160, B = 40, C = 205
2)
Let the total number of student be n
330 = n * ( 60 / 100)
n = 550
So there are 550 students in the school in total.
3)
98.5 * (112/100 ) ^ n > 300
(112/100 ) ^ n > 3000 / 985
(112/100 ) ^ n > 600 / 197
So 10 years later the share price will be over $300
2007-06-11 16:26:53 補充：
三題答得兩題，
仲要是最遲答的那個......
2007-06-10 9:25 pm
1. A + B + C = 405
A = 4B
B = A/4
C = A + 45
Solve A:
405 = A + A/4 + A+ 45
360 = 2A + 1/4 A
360 = 2.25A
A = 360/2.25
A = 160
B = A/4
B = 160/4
B = 40
C = A + 45
C = 160 + 45
C = 205
160 + 40 + 205 = 405
2. X = Total number of student in the school
0.6 X = 330
X = 330/0.6
X = 550
3. This is a compound interest question:
F = P (1 + r)^t
F = future value
P = Initial deposit
r = rate of increase per year
t = number of years
You are given:
F = 300, P = 98.5, r = 12%, solve t
300 < 98.5 (1 + 0.12)^t
300/98.5 < 1.12^t
1.12^t > 3.05
t = 10
A = 4B
B = A/4
C = A + 45
Solve A:
405 = A + A/4 + A+ 45
360 = 2A + 1/4 A
360 = 2.25A
A = 360/2.25
A = 160
B = A/4
B = 160/4
B = 40
C = A + 45
C = 160 + 45
C = 205
160 + 40 + 205 = 405
2. X = Total number of student in the school
0.6 X = 330
X = 330/0.6
X = 550
3. This is a compound interest question:
F = P (1 + r)^t
F = future value
P = Initial deposit
r = rate of increase per year
t = number of years
You are given:
F = 300, P = 98.5, r = 12%, solve t
300 < 98.5 (1 + 0.12)^t
300/98.5 < 1.12^t
1.12^t > 3.05
t = 10
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