There are two groups of numbers, the average number of the first group is 12.8, the average number of the second group is 10.2, and the total average number of these two groups is 12.02. What is the ratio of the number of the first group to the number of the second group

There are two groups of numbers, the average number of the first group is 12.8, the average number of the second group is 10.2, and the total average number of these two groups is 12.02. What is the ratio of the number of the first group to the number of the second group

The difference between the average of the first group and the total average of the two groups is as follows:
12.8－12.02＝0.78
The difference between the average of the second group and the total average of the two groups is as follows:
12.02－10.2＝1.82
78 × the number of the first group = 1. 82 × the number of the second group
The first group: the second group = 7:3
So the first group has 7 numbers (or multiples of 7 numbers), and the second group has 3 numbers (or multiples of 3 numbers)

The average of the three numbers is 5. The first one is 8. The second one is 1 larger than the third one. Find the third number

(5*3-8-1)/2=3

If the average of 10 numbers is 42, two of them are 10, then the average of the other 8 numbers is 42_____ .
2. The selling price of a, B and C candy is 5 yuan, 6 yuan and 7 yuan per 500 grams respectively. If 4000 grams of a candy, 3500 grams of B candy and 2500 grams of C candy are mixed together, the selling price should be set at 500 grams_________ Yuan

1.(42*10-20)/8=50
2. (4000 / 500) * 5 + (3500 / 500) * 6 + (2500 / 500) * 7 = 117 yuan