Question

英文数学题，请大家帮忙，谢谢！

Jeff bikes for three hours and his brother bikes four hours . although Jeff bikes 15 mph faster, his total distance was at most twice as far as his brother's ,how fast does each ride? 请大家写步骤！谢谢

Answer 1

你好
题意如下：Jeff 骑车三小时而他弟弟骑车四小时，虽然Jeff比他弟弟每小时快15英里，但他的总路程是他弟弟的两倍。他们的骑车速度分别是多少？
解法如下：suppose the speed of Jeff's brother is x mph
then Jeff‘s speed is x+15 mph
so (x+15)*3=2*x*4
3x+45=8x
5x=45
x=9
the speed of Jeff's brother is 9 mph
Jeff's speed is 24 mph
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Answer 2

Let Jeff bike x mph and his brother y mph. Then we have x=y+15, 3x< = 2 * 4y.
Take the equation to the inequation, we get 3y+45< = 8y, that is 45< =5y. Therefore y>=9. And this in turn gives us, from x=y+15, x<=24.
Hence，Jeff bikes at most 24 mph and his brother 9 mph.