The first question is in primary school, and the first question is in primary school

1 2000 can be simplified by hypothesis Hypothesis 1: (1+1 2+1 3)*(1 2+1 3+1 4)-(1+1 2+1 3+1 4)*(1 2+1 3) The result is 1 4 Hypothesis 2: (1+1 2+1 3+1 4)*(1 2+1 3+1 4+1 5)-(1+1 2+1 3+1 4+1 5)*(1 2+1 3+1 4) The result is 1 20 (1+1 2+1 3+.

1 1999) should be equal to 1 2000

Equal to 0 do not believe, you can ask someone.

Hello. 12 (days) A: It takes 12 days for the second team to cooperate.

Explanation: Team A does 1 20 of the whole project every day, Team B does 1 30 of the whole project every day, and the second team does it together, and completes (1 20 + 1 30) 5 60 of the whole project every day

The whole project is 1, and it takes several such "days", so you need to use division, 1 (1 20 + 1 30).

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Six points have 5+4+3+2+1=15 line segments. Hope.

The round bar is pulled out of the water, and the water surface of the bucket drops by 4 cm, that is: the volume of the round bar outgoing from the water is equal to the volume of the water falling.

The bottom area of the bucket: square centimeters.

When all the round bars are put into the water, the water surface rises by 9 centimeters, and the volume of water in the bucket rises equal to the volume of the round bar.

The volume of the round bar: 157 9 = 1413 cubic centimeters A: The volume of the round bar is 1413 cubic centimeters.

Column two equations: let the radius of the barrel be r and the height of the round bar be hIn the first case: 25 h = 9 r·r

In the second case, 25(h-8)=(9-4) r·r is solved in succession to find h = 18 cm.

First pull out 8 cm, the water surface drops 4 cm, then the bottom area of the bucket is 2 times that of round steel.

In addition, all the round steel is put into the bucket, and the water surface of the bucket rises by 9 cm, so the length of the round steel should be 18 cm.

With the cylindrical volume formula.

v=square*18=

Fill in the square 60 29 in turn, and the last one should be the number, first calculate 60 minus 50, then calculate 29 plus 10 to get 39

The ratio of the number of pears to apples in the fruit store is 3:2, and the number of pears in baskets is 3 2 After selling 15 baskets of pears on the same day, the number of apples in the basket accounts for 4 5 of the pears, so the number of pears in the basket is 5 4 of apples

Number of apple baskets = 15 (3 2-5 4) = 60 baskets of pears now = 60 5 4 = 75 baskets.

If the number of apple baskets is 2x, then the number of pears is 3x

2x/（3x-15）=4/5

10x=12x-60

x=30 for 60 baskets for apples and 90 baskets for pears.

The apple does not change, and the apple is seen as a unit "1", the first pear is 3 2 of the apple, and the second pear is the 5 4 of the apple There are: 15 (3 2-5 4) = 60 baskets.

Pears have: 60 3 2 = 90 baskets.

Now the pears are 90-15=75 baskets.

Number of apple baskets = 15 (3 2-5 4) = 60 baskets.

Now the pear = 60 5 4 = 75 baskets.