標題:

F.2 Maths 15分

發問:

Car A and Car B are 70km apart on a highway.It is given that cars A and B travel at a aonstant speed of akm/h and bkm/h recpectively.a.If cars A and B travel towards each other ,they will meet in 42 minutes. Write down an equation connecting a and b.b.If cars A and B travel towards the same each other, car B... 顯示更多 Car A and Car B are 70km apart on a highway.It is given that cars A and B travel at a aonstant speed of akm/h and bkm/h recpectively. a.If cars A and B travel towards each other ,they will meet in 42 minutes. Write down an equation connecting a and b. b.If cars A and B travel towards the same each other, car B will catch up with car A in 3hours and 30 minutes.Write down an equation connecting a and b. c.Hence find the values of a and b.

最佳解答:

I hope it is correct. Answer: a. 0.7(a+b) = 70 [Workings: 0.7h = 42/60min] b. 3.5b = 3.5a+70 [Workings: 3.5h=3+30/60min] c. a=40km/h, b=60km/h [Workings: 0.7(a+b) = 70 ...(1) 3.5b = 3.5a+70 ...(2) from (1) a+b = 70/0.7 a+b = 100 ...(3) from (2) 3.5a - 3.5b = -70 3.5(a - b) = -70 a - b = -20 ...(4) (3) - (4) a+b - (a-b) = 100 - (-20) 2b = 120 b = 60 sub b = 20 into (3) a+20 = 100 a = 40 ]

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