Logical Thinking in the interview-observation questions

1. There are two rooms, one of which has three lights, and the other has a switch to control the three lights. The two rooms are relatively independent and relatively closed, and there is no direct connection on the blank; the three lights are not necessarily related to the three switches in sequence. Now you can only enter the two rooms once, and then determine which switch controls the three lights respectively.
 
2. the 2x choir of the four-person group rushed to the concert venue, and they had to go through a bridge on the way. The sky was dark, while they only had one flashlight. At most two people can bridge the bridge at a time, while a flashlight must be held when crossing the bridge, so someone has to bring the flashlight back and forth at both ends of the bridge. A flashlight cannot be lost. The walking speed varies between the four people. If the two people walk with each other, the speed of the slow person prevails. A needs 1 minute to bridge the bridge, B needs 2 minutes to bridge the bridge, C needs 5 minutes to bridge the bridge, D needs 10 minutes to bridge the bridge, how do they bridge the bridge within 17 minutes?

3. There are 7 grams, 2 grams of each weight, one balance, how to use these items three times to divide 140 grams of salt into 50 grams, 90 grams each?

Reference answer:

1. Analysis: considering logic control alone, two switches can recognize at most two lights. Therefore, other approaches must be taken. The answer to this question is: heat, electric lamp fever. Go to the room with a switch, turn on the first switch for about 5 minutes, then turn off; then turn on the second switch. Then enter the room with lights. The hot and Closed Switch is the first switch; the light is the second switch; the light is the third switch.

PS: it cannot be determined logically. It must be integrated with common knowledge such as physical phenomena.

2. Analysis: reverse push method. Four people have to take five trips to complete the bridge. A 10-minute trip to D is required. That is to say, it takes only 7 minutes for the remaining four trips of the other three; that is to say, C cannot be in the remaining four trips, otherwise, there will be only two minutes for the remaining three trips. In fact, it will take at least three minutes for a to take three trips. In general, C and D must go together, and C cannot go back. Therefore, the answer is that a and B first pass, 2 minutes; A is back, 1 minute; C and D are over, 10 minutes; B is back, 2 minutes; A and B are together, 2 minutes. 17 minutes in total.

PS: digital analysis:
Select the sum of 5 numbers (repeatable) from 1, 2, 5, and 10 = 17. 17 = 10 + 2 + 2 + 2 + 1

3. analysis: for the first time, 140 grams are divided into two 70 grams, and 2 + 7 are called for the second time. 9 grams are obtained from one heap, for the third time, use the 9 grams and 2 grams of weight to weigh 11 grams from the same heap, and put the 9 + 11 = 20 grams in the opposite 70 grams of heap.

PS: Make full use of the balance and place salt on both sides. You can divide the balance into two equal portions by adding more and less supplements. In addition, the salt and weight can be replaced.

From the numerical point of view: 90 = 70 + 20 = 70 + 11 + 9 = 70 + 9 + 9 + 2 = 70 + (7 + 2) * 2 + 2

Reference: http://lin2x.blog.163.com/blog/static/1946601201042523344844/