You are Here: Home >< Maths

# Logical Maths Questions watch

1. A tank holds 20 gallons of water. When the tap over it is turned on water flows from it into the tank at a rate of 4 gallons a minute. When a plug in the bottom of the tank is pulled out water drains away from the tank at the rate of 6 gallons a minute.

1) With the tank empty and the plug in, the tap is turned on. How many minutes will it take to fill the tank?

I have the answer 5 minutes

2) With the tank full, the tap is turned on and the plug pulled out. How many minutes will it take to empty the tank?

I have the answer 10 minutes.

3) With the tank empty and the plug in, the tap is turned on for 3 minutes. It is then turned off and the plug pulled out. How many minutes will it then take to empty the tank?

I have the answer 2 minutes.

4) With the tank full, the plug is pulled out and the tap turned on. After 4 minutes the tap is turned off with the plug left out. How many more minutes will it take to empty the tank?

I have the answer 2 minutes.

5) The tank is full. The plug is pulled out for 2 minutes. The tap is then turned on for 3 minutes with the plug still out. How many gallons will be in the tank at the end of this time?

I have the answer 2 gallons.

6) The tank is empty with the plug in. The tap is turned on for 4 minutes. The plug is then pulled out with the tap left on for another 6 minutes. How manny gallons will be in the tank at the end of this time?

I have the answer 4 gallons.

Are the answer I obtained correct - have a missed something because this seems easy.

Number sequences:

1) 4, 9, 16, ... , 36, 49, 64 (25)

2) 2, 6, 12, ..., 30, 42, 56 (20)

3) 41, 38, 36, 33, ... , 28, 26, 23 (31)

4) 2, 3, 5, ..., 17, 33, 65 (9)

5) 3, 5, 4, 6, ..., 7, 6, 8, 7, (5)

6) 99, 80, 63, ..., 35, 24, 15 (48)

Are the (x) satisfy the (...) in the sequences?
2. Your answers can be either right or wrong...because the questions are impossible to answer since you have no idea how big the tank is other than it's at least 20 gallons. xD
3. (Original post by WeiChin)
Your answers can be either right or wrong...because the questions are impossible to answer since you have no idea how big the tank is other than it's at least 20 gallons. xD
No there are definitely answers to these questions and I disagree with you.
4. So I guess no one knows the answers? wtf...lol?
5. All looks fine to me!
6. I got 14 for question 5. The same for all the others though...
8. (Original post by I'm clever)
A tank holds 20 gallons of water. When the tap over it is turned on water flows from it into the tank at a rate of 4 gallons a minute. When a plug in the bottom of the tank is pulled out water drains away from the tank at the rate of 6 gallons a minute.

1) With the tank empty and the plug in, the tap is turned on. How many minutes will it take to fill the tank?

I have the answer 5 minutes CORRECT

2) With the tank full, the tap is turned on and the plug pulled out. How many minutes will it take to empty the tank?

I have the answer 10 minutes. CORRECT

3) With the tank empty and the plug in, the tap is turned on for 3 minutes. It is then turned off and the plug pulled out. How many minutes will it then take to empty the tank?

I have the answer 2 minutes. CORRECT

4) With the tank full, the plug is pulled out and the tap turned on. After 4 minutes the tap is turned off with the plug left out. How many more minutes will it take to empty the tank?

I have the answer 2 minutes. CORRECT

5) The tank is full. The plug is pulled out for 2 minutes. The tap is then turned on for 3 minutes with the plug still out. How many gallons will be in the tank at the end of this time?

I have the answer 2 gallons. CORRECT

6) The tank is empty with the plug in. The tap is turned on for 4 minutes. The plug is then pulled out with the tap left on for another 6 minutes. How manny gallons will be in the tank at the end of this time?

I have the answer 4 gallons. CORRECT

Are the answer I obtained correct - have a missed something because this seems easy.

First, the tank holds 20 gallons, lets call this an absolute value.

With the rate of flow from the tap being 4gpm, and the capacity of the tank being 20 gallons, the tanks capacity after 4 minutes will be 16 gallons.

With the rate of loss with the tap on (4gpm) and plug out (-6gpm) being -2gpm then over 6 minutes you will lose 12 gallons from the original 16 in the tank!

PS: I went thru the calculation to the last one as it seemed to me to be wrong on my first 4 looks at it. And now I have a headache!!! NEED COFFEE !!!
9. (Original post by spliishie)
I got 14 for question 5. The same for all the others though...
Q5) The tank is full implies it has 20 Gallons of water in it. The plug is pulled out for 2 minutes. If water leaves the tank at a rate of 6 gallons every minute there will be at this point. The tap is then turned on for 3 minutes with the plug OUT. The water leaves the tank at a rate of 6 gallons and enters at a rate of 4 gallons. Therefore water leaves the tank at a rate of Over 3 minutes -> leaves in 3 minutes. Therefore the amount left in the tank is 8-6=2 gallons.

Is that right?
10. (Original post by I'm clever)
Q5) The tank is full implies it has 20 Gallons of water in it. The plug is pulled out for 2 minutes. If water leaves the tank at a rate of 6 gallons every minute there will be at this point. The tap is then turned on for 3 minutes with the plug OUT. The water leaves the tank at a rate of 6 gallons and enters at a rate of 4 gallons. Therefore water leaves the tank at a rate of Over 3 minutes -> leaves in 3 minutes. Therefore the amount left in the tank is 8-6=2 gallons.

Is that right?
Yeah that's right. Mustn't have been thinking, I added the final 6 instead of subtracting it for some reason.
Yeah that's right. No they don't seem too difficult do they? :

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: April 8, 2011
Today on TSR

### Congratulations to Harry and Meghan!

But did you bother to watch?

Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams