我個表弟數學題, 一個小學題好深,
Jason saved some money to buy a toy plane. During the first week, he saved 1/4 of the price of the toy plane. In the second week, he saved $48 more than teh amount he had saved in the first week. In the third week, he saved $159 more than the amount he had saved in the first week. After the third week, he realised that he had $20 more than the price of the toy plane. Find the cost of the toy plane.
小學數學題
2010-12-23 12:30 am
回答 (4)
2010-12-23 12:37 am
✔ 最佳答案
Let the cost of the toy plane be x.Total amount of savings=x+20
First week saves: x/4
Second week saves: x/4+48
Third week saves: x/4+159
x/4+(x/4+48)+(x/4+159)=x+20
3x/4+207=x+20
187=x/4
x=748
The cost of the toy plane=$748
2010-12-23 8:13 am
2010-12-23 1:15 am
Ahhh.. let me try this one in English format.
1st week (ended)
- save 1/4 cost of plane
2nd week (ended)
- save 1/4 cost of plane +$48 (extra information?!)
3rd week (ended)
- save 1/4 cost of plane + 159
after 3rd week (I'm assuming end of 3rd week = after 3rd week)
he had $20+ cost of plane
so... $20 + cost of plane = 1/4 of plane + $159
therefore : 3/4 cost of plane = $139
Cost of plane = (4x139)/3 = $183.33 (oops!) decimal
Got a feeling it's wrong, can someone explain?
2010-12-22 17:36:47 補充：
Ok.. I understand now after seeing others do their sum. But they should re-phrase the sentence to : net savings for the 2nd/3rd week alone, otherwise it would be could be presume that savings are snow-ball.
(lol)
got it wrong and arguing on langauge.
1st week (ended)
- save 1/4 cost of plane
2nd week (ended)
- save 1/4 cost of plane +$48 (extra information?!)
3rd week (ended)
- save 1/4 cost of plane + 159
after 3rd week (I'm assuming end of 3rd week = after 3rd week)
he had $20+ cost of plane
so... $20 + cost of plane = 1/4 of plane + $159
therefore : 3/4 cost of plane = $139
Cost of plane = (4x139)/3 = $183.33 (oops!) decimal
Got a feeling it's wrong, can someone explain?
2010-12-22 17:36:47 補充：
Ok.. I understand now after seeing others do their sum. But they should re-phrase the sentence to : net savings for the 2nd/3rd week alone, otherwise it would be could be presume that savings are snow-ball.
(lol)
got it wrong and arguing on langauge.
2010-12-23 12:41 am
Let $x be the cost of the toy
0.25x+(0.25x+48)+(0.25x+159)-20=x
0.75x+48+159-20=x
0.75x+187=x
0.25x=187
x=748
Therefor,the cost of the toy is$748
0.25x+(0.25x+48)+(0.25x+159)-20=x
0.75x+48+159-20=x
0.75x+187=x
0.25x=187
x=748
Therefor,the cost of the toy is$748
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