3題f.1 數學題...急

2007-12-02 7:09 am

David has three types of banknotes, $10-note, $20-note and $50-note in his wallet. The number of $20-notes is less than that of $10-notes by 5, while the number of $50-notes is more than half of the number of $20-notes by 7. If David has 22 banknotes altogether, find the number of each type of banknotes in his wallet.

更新1:

Ken 's age is half of his father 's age now.Eight year later ,Ken's father will be 60 years old .Find the present age of Ken age. If the sum of 3 consecutive odd numbers is 39,find the value of the smallest odd numbers

更新2:

要有步驟...(唔好太複雜）ｔｈｘ．．．

更新3:

To:o0Kai0o 唔係好明第1題wo....可唔可以再easy d? THZ

回答 (1)

[匿名]

2007-12-02 9:06 pm

✔ 最佳答案

1) Let x, y, z be the number of $10-note, $20-note and $50-note in his wallet respectively
x+y+z=22---(1)
x-5=y---(2)
z-7=y/2---(3)

From (2), x=y+5---(2) '
From (3), z=y/2+7---(3) '

Sub (2) ', (3) ' into (1),
(5/2)y=10
y=4
Sub y=4 into (2)
x=9
Sub y=4 into (3)
z=9

2) Let x, y be Ken's and his father's present age respectively
2x=y---(1)
y+8=60---(2)
From (2), y=52
Sub y=52 into (1)
x=26

3) Let x be the smallest odd numbers
x+x+2+x+4=39
3x=33
x=11

P.S. 每題最尾果句自己寫番...

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