1, there are four numbers: A, B, C and D, and the sum of A and B is 68.6; The sum of b and c is 39.7; The sum of c and a is 71.5; The sum of b and d is 40. What are these four numbers?

Solution: The sum of numbers A, B and C is: (68.6+39.7+71.5) ÷ 2 =179.8 ÷ 2 = 89.9,

Get A = sum of three numbers-sum of b and c =89.9-39.7=50.2,

B =, sum of three numbers -A, sum of C =89.9-7 1.5= 18.4,

C = sum of a and c-a = 71.5-50.2 = 21.3,

D = B, and the sum of D-B =40- 18.4=2 1.6.

2. There are two goldfish bowls. If you take 15 tails out of the first tank and put them in the second tank, the goldfish in the first tank is exactly 3/4 of that in the second tank. If 17 tails are taken out of the second tank and put into the first tank, the goldfish in the second tank is exactly 4/ 1 1 of the first tank.

Solution: As shown in the figure,

Analysis:

The total number of fish in the two tanks remains the same.

Take out the first cylinder 15 tail and put it into the second cylinder, and the rest of the first cylinder is 3/4 of the second cylinder, that is, 3/(3+4) = 3/7 of the total;

The tail of 17 from the second cylinder is put into the first cylinder, and the rest of the second cylinder is 4/1of the first cylinder, that is, the rest of the second cylinder is 4/(4+ 1 1) of the total, so that the first cylinder is/kloc-0 of the total.

There are more fish in the first tank for the second time than for the first time: 15+ 17 = 32 (tail)

And its share in the total has increased:1115-3/7 = 32/105.

Therefore, the total number of fish in two tanks: 32 ÷ (32/ 105) = 105 (tail)

After the first cylinder takes out 15 tail, it is: 105× 3/7 = 45 (tail).

So, the result is: 45+ 15 = 60 (articles)

Check calculation: the second cylinder was originally: 105-60 = 45 tails);

After giving the first cylinder 17 tails, there are 28 tails left. The first cylinder is; 60+ 17 = 77 tails),

28/77 = 4/ 1 1, which is in line with the meaning of the question.