小學數學題!!!

1)
A water tank is two-fifth full. Pipe A can fill a tank in 10 minutes and pipe Bcan empty it in 6 minutes. If both the pipes are open, howlong will it take to empty or fill the tank completely?
1.) 6 min. to empty 2.) 6 min. to fill 3.) 9 min. to empty 4. ) 9 min. to fill5.) None of these?

The answer is: 1.) 6 min to empty

In one min, pipe A fills 1/10 of the tank, and pipe B empties 1/6 of the tank.
Since 1/6 > 1/10, the tank will be emptied when both the pipes are open.
The tank is only 2/5 full.
Time taken to empty the tank = (2/5) ÷ [(1/6) - (1/10) min = 6 min


= = = = =
2)Adoes a work in 10 days and B does the same work in 15 days. in how many daysthey together will do the same work?
1. 5days 2. 6days 3. 8days 4. 9days?

The answer is: 2. 6days

In each day, A does 1/10 of the work, and B does 1/15 of the work.
When the work together, they do [(1/10) + (1/15)] = 1/6 of the work
No. of days needed = 1 ÷ (1/6) = 6

很多人少時候都學奧數，有人學得好，有人學得差。

憑現今的表現可以推想當年學奧數學得一團糟。

1.

A=25/10
B=25/6

2.5+4.16=6.66667

25/6.66667=3.74999999999

A work = 1/10 per day
B worl = 1/15per day


0.1+0.06=0.16
1/0.16=6.25
要6.25日

我好細個小學學奧數,好淺