中二ｒａｔｅ　ａｎｄ　ｒａｔｉｏ問題，ｐｌｚ　ｈｅｌｐ！

A tank canbe filled up in 2 h 30min when 3 taps are turned on. How long does it take to fill up the same tank when 5 taps are turned up?
since the time is designed by the number of tap,
if no mention,we design that there is a relationship between time and no.of tap is
always constant
so,we set up this formula
let t min be the time used when 5 taps are turned on:
(2 x 60 + 30)(3) = 5t
450 = 5t
t = 90
so,it uses 90 mins(or 1 hour 30 mins)


A piece of work can be completed by x people in 10 days. If 1 more person is added, the work can be completed in 8 days. What is the value of x?
the explaination is same as above
10x = 8(x + 1)
10x = 8x + 8
2x = 8
x = 4
so,there are 4 people

2 h 30min =150min
Let t be the time required
150:t=5:3
t=90=1hr and 30min

2:
x:x+1=8:10
X=4

In two questions mentioned above, the ratio is reversed as the first factor is proportional to the reciprocal of the second factor