蜡烛每分钟烧掉的长度一定,8分钟后蜡烛长12cm,18分钟后蜡烛长7cm,问蜡烛最初有多长?
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蜡烛每分钟烧掉的长度一定,8分钟后蜡烛长12cm,18分钟后蜡烛长7cm,问蜡烛最初有多长?
蜡烛每分钟烧掉的长度一定,8分钟后蜡烛长12cm,18分钟后蜡烛长7cm,问蜡烛最初有多长?
蜡烛每分钟烧掉的长度一定,8分钟后蜡烛长12cm,18分钟后蜡烛长7cm,问蜡烛最初有多长?
蜡烛缩短所用时间：18-8=10(分钟)
蜡烛缩短的长度为：12-7=5（cm）
所以蜡烛每分钟燃烧的长度为：5/10=0.5（cm/分钟）
前8分钟蜡烛烧掉的长度即为：0.5X8=4cm
所以蜡烛原来的长度为：4+12=16cm
答：蜡烛最初有16cm长
1分钟烧(12-7)÷(18-8)=0.5厘米
所以原来12+8×0.5=16厘米
方法一：设蜡烛最初长度为X，每分钟烧掉长度为Y
X-8Y=12
X-18Y=7
2式相减 10Y=5 Y=0.5
X=16
方法二：十分钟烧掉了5厘米 一分钟烧掉了0.5里面 点火8分钟烧掉了4里面 加上12厘米原长就是16呗。
答案是16cm
（12-7）除以（18-8）=1/2
1/2乘以 8=4
4+12=16
（12-7）/（18-8）8+12=16。
用方程：设蜡烛原长X厘米，每分钟燃烧Y厘米，于是
X-8Y=12
X-18Y=7
蜡烛最初有16cm
(12-7)÷(18-8)=0.5厘米
所以原来12+8×0.5=16厘米
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