數學方程式（英文）急!!!

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2011-11-20 12:10 am

12.The total price of 24 books is$405.Some of them are sold at $15 each and the other at each.Find the number of books that are sold at $15 each.

13.York has $72.Sally has $12.in order to let Sally have 3 times the amount of York,how much should York give Sally?

14.A sum of money is planned to be evenly shared among 10 persons.Due to the absence of 2 persons,each person present can get $30 more.Find the sum of money.

15.Carl has $9 more than David does.Hilbert has 1/3 of the amount of Carl.If they have a total amount of $61,how much does each of them have?

16.There are 42 students in S1a.The number of the boys is4/3 times that of girls.Find the respective number of boys and girls there.

17. 72 marbles are divided into two groups.7times the number of marbles in the smaller group is equal to 5 times that in larger groups.Find the number of marbles in the smaller group.

18.The total age of Hebrew and his son is 51.3years ago,hebrew is 8times as old as his son.Find the current age of Hebrew's son.

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回答 (1)

william

2011-11-20 3:32 am

✔ 最佳答案

12. what is the price of the other ?

the formula is 15 * X + (24-X) * P = 405 (where X be the no. of
the books sold at $15, and P be the price of the other)

13.
let X be the amount that York give to Sally

72 - X = 3 * (12 + X)
72 - X = 36 + 3X
72 - 36 = 3X + X
36 = 4X
X = 9

14.
let X be the sum of money

X/8 - X/10 = 30
40 * (X/8 - X/10) = 30 * 40
5X - 4X = 1200
X = 1200

15.
let Carl has $X

X + X - 9 + X/3 = 61
3 * (X + X - 9 + X/3) = 61 * 3
3X + 3X - 27 + X = 183
7X = 163 + 27
7X = 210
X = 30

Ans : Carl has $30, David has $21 and Hilbert has $10

16.
let G be the no. of girls

G + 4G/3 = 42
3G + 4G = 42 * 3
7G = 126
G = 18
hence, no. of boys = 42 - 18 = 24

17.
let X be the no. of marbles in small groulp

X + 7X/5 = 72
5X + 7X = 72 * 5
12X = 360
X = 30

18.
let X be current age of Hebrew's son

(51 - X - 3) = 8 * (X - 3)
48 - X = 8X - 24
48 + 24 = 8X + X
72 = 9X
8 = X
X = 8

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