Topic content:
In order to save water, a city has made the following provisions on the charging standard of tap water: 2 yuan/ton will be charged for the part of each household whose water consumption does not exceed 10 tons per month; The part exceeding 10 tons but not exceeding 20 tons will be charged at 2.5 yuan/ton; The part exceeding 20 tons will be charged at 4 yuan/ton
(1) Xiang Shijia used 16 tons of water in May and asked how much the water fee should be paid
(2) Mr. Wu's family paid 69 yuan for water in May, and asked how many tons of water they used in May
(3) If Mr. Wu's family uses a ton of water in June, how much should he pay for water? (expressed by the algebraic expression of a)
Best answer:
(1) 10 × 2+(16-10) × 2.5=20+15=35 yuan;
(2) Solution 1: ∨ 10 × 2+(20-10) × 2.5=45 < 69
Teacher Wu's family used more than 20 tons of water in May
The water consumption of Mr. Wu's family in May is 20+69-454=26 (tons);
Solution 2: Let Teacher Wu's house use x tons of water in May
∵10×2+(20-10)×2.5=45<69。
Teacher Wu's family used more than 20 tons of water in May.
∴45+4(x-20)=69。
The solution is x=26.
Answer: Mr. Wu's family used 26 tons of water in May
(3) ① When 0 < a ≤ 10.
The payable water fee is 2a yuan.
② When 10 < a ≤ 20.
The payable water fee is 20+2.5 (a-10)=2.5a-5 (yuan).
③ When a > 20.
The payable water fee is: 20+2.5 (20-10)+4 (a-20)=4a-35 (yuan)
Answer analysis:
69-454
Test core:
Positive Number: negative number (real number) greater than 0: negative number (real number) less than 0 is neither positive nor negative.
Non negative number: positive number and zero. Non positive number: negative number and zero.