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Logical Questions

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?