Mrs Chan buys some candies at $1 and $2. If she spends $27 altogether and gets 20 candies, how many $2 candies does she buy?
陳太買一些$1及一些$2的糖果。如果她一共用去$27買了20粒糖果，她共買了多少粒$2的糖果?
數學題(未知數)
2009-07-10 7:39 am
回答 (2)
2009-07-10 7:44 am
✔ 最佳答案
let x be the number of $2 candies and y be the number of $1 candiesThere are two equations:
1. 2x + y = 27
2. x + y = 20
(1) - (2)
x=7
so y = 13
Mrs Chan buy 7 pcs $2 candies and 13pcs $1 candies.
2009-07-10 8:35 am
Let x be the candies at $1 and y be the candies at $2
x + y= 20 (1)
1x + 2y = 27 (2)
From (1) , x = 20 - y (3)
P.S. <It becomes (3) even just the change in form of the equation.>
Sub (3) into (2)
1(20 - y) + 2y = 27
20 - y + 2y = 27
y = 27 - 20
y =7
Therefore, she buys 7 of the $2 candies.
x + y= 20 (1)
1x + 2y = 27 (2)
From (1) , x = 20 - y (3)
P.S. <It becomes (3) even just the change in form of the equation.>
Sub (3) into (2)
1(20 - y) + 2y = 27
20 - y + 2y = 27
y = 27 - 20
y =7
Therefore, she buys 7 of the $2 candies.
參考: by myself
收錄日期: 2021-05-01 09:44:50
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