1. 72marbles are divided into two potions so that 7 times the smaller portion equals 5 times the bigger portion . Find the number of marbles in the smaller portion .
2.The cost of 24 books is $405 . Among them , some cost $15 each and all the others cost $20 each . What is the number of books whose cost is $15 ?
Maths questions (F.1)
2008-06-05 5:40 am
回答 (2)
2008-06-06 4:55 am
✔ 最佳答案
1.Let the number of marbles in the smaller portion be xthe number of marbles in the bigger portion be (72-x)
7x = 5(72-x)
7x = 360-5x
12x = 360
x=30
The number of marbles in the smaller portion is 30.
2.Let the number of books whose cost is $15 be x
the number of books whose cost is $20 be (24-x)
15x+(24-x)20 = 405
-5x = -75
x = 15
The number of books whose cost is $15 is 15.
2008-06-05 20:57:48 補充：
7 times the smaller portion equals 5 times the bigger portion
代數就知 : 7(30) = 5(72-30)
210 = 5(42)
210 = 210
參考: 自己
2008-06-05 5:59 am
1.
IF the smaller portion is a,then the bigger portion is 5a
then
a 5a=72
a=12
the number of marbles in the smaller portion is 12marbles.
2.
If some of them cost$15 that is m,then the others that cost$20 is 24-a
then
15a 20(24-a)=405
15a 480-20a=405
480-405=20a-15a
75=5a
a=15
the number of books whose cost is $15 is 15
IF the smaller portion is a,then the bigger portion is 5a
then
a 5a=72
a=12
the number of marbles in the smaller portion is 12marbles.
2.
If some of them cost$15 that is m,then the others that cost$20 is 24-a
then
15a 20(24-a)=405
15a 480-20a=405
480-405=20a-15a
75=5a
a=15
the number of books whose cost is $15 is 15
參考: all by myself
收錄日期: 2021-05-01 16:08:34
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