1). Two cars travelling in opposite directions at speeds 65 km/h and 60 km/h respectively meet on a straight road. After at least how many minutes will their minimum distance be 5 km?
2). Dick has 22 coins. Each conin is either a $2 coin or $5 coin. The total value of the coins is more thatn $83. Find the maximum number of $2 coins that Dick has.
linear inequalities in one unknown ---- urgent
2007-11-26 2:18 am
回答 (2)
2007-11-26 2:39 am
✔ 最佳答案
1) (65+60)km/h X a hours = 5km
a = 0.04 hours
> 0.04 * 60mins = 2.4 mins
2)
2*a+5*(22-a) = 83
2a+110-5a = 83
a = 9
Max. no, of $2 coins is 9
2007-11-25 18:46:17 補充：
Please noted that two cars are travelling in opposite direction, sothe speed is (65 60)km/h.if the cars are travelling in same direction, the speed is (65-60)km/hask yourself, is it make sences if a car takes 1 hours to travel 5km?
2007-11-26 2:29 am
Let x be the number of miniutes that the distance would be at least 5 km.
(65/60)x - (60/60)x >= 5
13x/12 - x >= 5
x/12 >= 5
x >= 60
At least 60 minutes will their minimum distance to be 5 km.
2. Let x be the number of $2 coins.
2x + (22-x)(5) > 83
2x + 110 - 5x > 83
-3x > -27
x < 9
The maximum number of $2 coins is 8.
2007-11-25 18:44:23 補充：
Sorry, i make a mistake in Q1.The equation should be(65/60)x + (60/60)x >= 513x/12 + x >= 525x/12 >= 525x >= 60x >= 60/25x >= 2.4 Therefore, at least 2.4 minutes will their minimum distance to be 5 km.
(65/60)x - (60/60)x >= 5
13x/12 - x >= 5
x/12 >= 5
x >= 60
At least 60 minutes will their minimum distance to be 5 km.
2. Let x be the number of $2 coins.
2x + (22-x)(5) > 83
2x + 110 - 5x > 83
-3x > -27
x < 9
The maximum number of $2 coins is 8.
2007-11-25 18:44:23 補充：
Sorry, i make a mistake in Q1.The equation should be(65/60)x + (60/60)x >= 513x/12 + x >= 525x/12 >= 525x >= 60x >= 60/25x >= 2.4 Therefore, at least 2.4 minutes will their minimum distance to be 5 km.
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