一元一次方程式

設:香港至廣州為 X km

x /4 + x/3 = 91

x = 156 km

Let 距離 = Ykm:

Y/4 + Y/3 = 19
3Y/12 + 4Y/12 = 19
7Y = 91 x 12
Y = 1092 / 7
Y = 156

Let x be the distance from Hong Kong to Guang Zhou
Let y be the time taken by愛德華 to run from Hong Kong to Guang Zhou with speed 4km/h

4y=x...(1)
3(91-y)=x.....(2)

Put x=4y into (2)

3(91-y)=(4y)
273-3y=4y
7y=273
y=39

so he uses 39hours for the first journey and 91-39=52hours for the second journey.

Put y=39 into (1)
4(39)=x
x=156
so the distance from Hong Kong to Gunag Zhou is 156km.