Solutions; Let the number in the tenth place be x, the number in the hundredth place be x+7, and the number in the unit place be 3X.
x+x+7+3x= 17
5x= 10
x=2
The number of digits is 2, the number of digits is 2+7=9 and the number of digits is 3X2=6.
This three-digit number is: 926.
(2) A city charges a monthly water fee according to the following provisions, with the water consumption not exceeding 6 tons, and the fee per ton is 1.2 yuan; If it exceeds 6 tons, the part that does not exceed will still be charged per ton 1.2 yuan, and the part that exceeds will be charged per ton of 2 yuan. If a user's water fee in May averages per ton 1.4 yuan, what is the user's pressure water fee in May?
Solution: Suppose this user's water consumption in May is X tons.
6X 1.2+(x-6)2= 1.4x
7.2+2x- 12= 1.4x
0.6x=4.8
x=8
User's pressure water fee in May:1.4x8 =11.2 yuan.
(3) Xiaohua's mother bought a shirt and a pair of trousers for her father, which cost 306 yuan. Among them, shirts are 30% off the list price, pants are 20% off the list price, shirts are listed in 300 yuan, so what is the list price of pants?
Solution: Let the price of trousers be X yuan.
0.8x+300x0.7=306
0.8x+2 10=306
0.8x=96
x= 120
(4) A shopping mall plans to sell 900 computers every month. During the golden week from June to 10, and from 1 to July, the mall decided to carry out promotional activities, and the sales plan for10 increased by 30% in June. It is known that 54 sets are sold every day for 7 days in Golden Week, so how many sets are sold every day for 24 days after this month to complete this month's plan?
Solution: Suppose this player sells at least X units a day on average after playing for 24 days this month to complete this month's plan.
24X+7x54=900x( 1+30%)
24x+378= 1 170
24x=792
x=33