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?
来源:学生作业帮助网 编辑:作业帮 时间:2024/07/28 12:10:18
![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?](/uploads/image/z/4341818-2-8.jpg?t=%E8%9C%A1%E7%83%9B%E6%AF%8F%E5%88%86%E9%92%9F%E7%83%A7%E6%8E%89%E7%9A%84%E9%95%BF%E5%BA%A6%E4%B8%80%E5%AE%9A%2C8%E5%88%86%E9%92%9F%E5%90%8E%E8%9C%A1%E7%83%9B%E9%95%BF12cm%2C18%E5%88%86%E9%92%9F%E5%90%8E%E8%9C%A1%E7%83%9B%E9%95%BF7cm%2C%E9%97%AE%E8%9C%A1%E7%83%9B%E6%9C%80%E5%88%9D%E6%9C%89%E5%A4%9A%E9%95%BF%3F)
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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