Primary 2 math problems, Primary 2 math problems, help solve them.?

Up to nine times At least three times The most cases can only happen when you are at a low level: you try all four keys in the first room, and the door is opened the fourth time; In the second room, you try the remaining three keys before opening the door; In the third room, you try the remaining two before you open the door; The last room is, of course, the last key left, 4+3+2. The probability of this happening is 1+1+1+1 smaller than when I go out and pick up dollars for a week.

The least of the time you try one of the best, and each time you get the key just enough to open your room.

Up to 10 times.

Try the first door up to 4 times, the second door up to 3 times, the third door up to 2 times, and the fourth door no longer have to be tried.

Minimum 3 times. The first three doors were opened in one go, and the fourth door didn't have to be tried.

29 times. The first door should be tried up to 16 times, the second door should be tried up to 9 times, the third door should be tried up to 4 times, and the fourth door should not be tried.

16 times, because each key has to be opened 4 times, there are 4 keys, so 4*4 is not = 16? The opinion is the same

I hope you study hard and make progress every day!

3 + 2 + 1 = 6 times.

If the first three are not, it must be the fourth.

Times. If the first three are correct, the fourth one doesn't need to be tried.

Xiao Ming has 5 pieces of sugar, Xiao Li's number of auspicious pieces is 3 times that of Xiao Ming, how many pieces of sugar does Xiao Li have? Feast.

5 3 15 (pieces).

A: Xiaoli, there are 15 pieces of sugar.

Summary. Kiss, tell us about your problem<>

Kiss, tell us about your problem<>

Kiss, do you have any questions about the first three questions?

Kiss, this analysis is a little more troublesome, you can choose Xun orange to choose a bad business card, which also saves your time, and it can also be easier to bend the white question of the <>

I can understand.

The middle 60 centimeters are dry, and the 40 centimeters are wet, and the wet part is divided into two parts, so divide by two and you're 20 centimeters, so the puddle is 20 centimeters deep, which is still a little deep, after all, it's about the size of a ruler, and it's going to get wet when you step into it.

1m=100cm

The wet part = the total length of the stick - the dry part.

Wet part 100-60 = 40 (cm).

The wet portion = 2 times the puddle depth.

Puddle depth 40 2 = 20 (cm) = 2 (dm).

The length of the bamboo pole minus the unwet part.

100-60=40(cm)

Because it is put into the water twice, the length of the two submersions is the same.

40÷2=20(cm)