『10分』F.1 maths (ratio)

Find the value of each of the following unknowns.

1) d days : 3 weeks = 8 days : 3 weeks and 3 days
[Solution: 1 week = 7 days]

回答:
d days : 3 weeks = 8 days : 3 weeks and 3 days
d days : 3 x 7 days = 8 days : 3 x 7 + 3 days
d days : 21 days = 8 days : 21 + 3 days
d days : 21 days = 8 days : 24 days
d / 21 = 8 / 24 *[ " / " mean "over", you need to remember in ratio x : y = x / y]
d / 21 = 1 / 3
d = ( 1 / 3 ) ( 21)
d = 7

∴The unknown value of d is 7.

2007-04-27 20:25:47 補充：
delete all the computer mistakes " &quot "," / " is meaning mathematic "over".

d days : 3 weeks = 8 days : 3 weeks and 3 days
d days : 3x7 days = 8 days : 3x7+3 days
d days : 21 days = 8 days : 24 days
24d days = 168 days (交叉相乘）
d days = 168/24 days
d = 7 days


明唔明呀？

2007-04-27 22:53:14 補充：
d days : 3 weeks = 8 days : 3 weeks and 3 daysis the same as d days / 3 weeks = 8 days / 3 weeks and 3 days

d days : 3 weeks = 8 days : 3 weeks and 3 days
d days : 3 weeks = 8 days : 3x7+3 days
d days : 3x7 days= 8 days : 24 days
d days= 8 days : 24 days x 21 days
d days= 7 days
d= 7

d days :21days = 8 days : 24days

d days :21days = 1:3

d /21 =1/3

d =7