2. The two brothers are 15 and 9 years old respectively this year. How many years later, my brother is twice as old as my brother?
3. Pour the water in a cuboid iron box filled with water into a cylindrical bucket with an inner diameter of 200mm. The length, width and height of the water in the iron box are 300mm, 300mm and 80mm respectively. Just fill it up and find the height of the cylindrical bucket (accurate to 0. 1mm, ≈ 3. 14).
A train must cross the first and second iron bridges at a speed of 600 meters per minute. It takes 5 seconds longer to cross the second iron bridge than the first one, and knowing that the length of the second iron bridge is 50 meters shorter than that of the first one, try to find the length of each iron bridge.
5. There is a 50g tricolor ice cream, and the proportion of brown, red and white ingredients is 2: 3: 5. How many grams of brown, red and white ingredients does this tricolor ice cream have?
6. There are 16 workers in a workshop, and each person can process 5 parts A or 4 parts B every day. Of these 16 workers, some process parts A and the rest process parts B. It is known that each part A can make a profit 16 yuan, and each part B can make a profit in 24 yuan. If this workshop makes money,
7. The basic price of domestic electricity for residents in a certain area is 0.40 yuan per kWh. If the monthly electricity consumption exceeds one kWh, the excess will be charged at 70% of the basic electricity price.
(1) a household used 84 kwh of electricity in August, and * * * paid 30.72 yuan for electricity, so it was a.
(2) If the average electricity bill of users in September is 0.36 yuan, how many kilowatts of electricity will be used in September? How much should I pay for the electricity?
8. An appliance store plans to buy 50 TV sets from manufacturers for 90,000 yuan. It is known that this manufacturer produces three different models of TV sets, with ex-factory prices of A 1.500 yuan, B 2 1.000 Yuan and C 2500 Yuan respectively.
(1) If the appliance store buys 50 sets of two different models of TV sets at the same time, which costs 90,000 yuan, please study the purchase scheme of the store.
(2) If a shopping mall sells a model A TV set with a profit of 150 yuan, a model B TV set with a profit of 200 yuan and a model C TV set with a profit of 250 yuan, and buys two different TV sets at the same time, which scheme is the most profitable?
answer
1. Solution: It takes X hours for Party A and Party B to complete the work together.
According to the meaning, x+(+) x = 1.
Solve this equation and get x=
=2 hours 12 minutes
A: It will take two hours for Party A and Party B to complete this work together.
2. solution: suppose that after x years, my brother is twice as old as my brother.
X years later, the elder brother's age is 15+x, and the younger brother's age is 9+X.
2×(9+x)= 15+x From the meaning of the question.
18+2x= 15+x，2x-x= 15- 18
∴x=-3
Three years ago, my brother was twice as old as my brother.
(Note: The meaning of three years is not meaningless, but refers to the three years before this year as the starting point, as opposed to the amount after three years)
3. Solution: Let the height of cylindrical barrel be x mm..
()2x=300×300×80
X is about 229.3
Answer: The height of the cylindrical bucket is about 229.3 mm. 。
4. Solution: If the length of the first iron bridge is x meters, the length of the second iron bridge is (2x-50) meters, and the time required to cross the first iron bridge is minutes.
It takes several minutes to cross the second railway bridge.
According to the meaning of the question, you can list the equations.
+ =
Solve the equation x+50=2x-50.
Get x= 100.
∴2x-50=2× 100-50= 150
Answer: The length of the first railway bridge is 100 meters, and the length of the second railway bridge is 150 meters.
5. Solution: Make the brown content in this tri-color ice cream 2x grams.
Then the red and white materials are 3 grams and 5 grams respectively.
According to the question, 2x+3x+5x=50.
Solve this equation and get x=5.
So 2x= 10, 3x= 15, 5x=25.
A: The ingredients of this tri-color ice cream are 10g, 15g and 25g respectively.
6. solution: suppose there are x workers processing part a on this day.
Then five A-type parts and four (16-x) B-type parts were processed on this day.
According to the meaning of the question, it is16× 5x+24× 4 (16-x) =1440.
The solution is x=6.
A: There are six workers processing Class A parts on this day.
7. Solution: (1) From the meaning of the question, you get.
0.4a+(84-a)×0.40×70%=30.72
The solution is a=60.
(2) If the electricity consumption in September is X kWh, then
0.40×60+(x-60)×0.40×70%=0.36x
The solution is x=90.
So 0.36×90=32.40 (yuan)
A: In September, * * * used 90 degrees of electricity, and the electricity bill payable was 32.40 yuan.
8. Solution: Calculate the A and C TVs respectively according to the three schemes of buying A and B TVs and B and C TVs.
If you buy X A-type TVs and Y B-type TVs.
(1)① When buying two kinds of TV sets, A and B, and B buys (50-x) sets, the equation can be obtained.
1500 x+2 100(50-x)= 90000
That is 5x+7(50-x)=300.
2x=50
x=25
50 x = 25
(2) When buying two kinds of TV sets, A and C, C will buy (50-x) sets.
The equation 1500x+2500(50-x)=90000 can be obtained.
3x+5(50-x)= 1800
x=35
50-x= 15
③ When buying B and C TV sets, the C TV set is (50-y).
Equation 2 100y+2500(50-y)=90000 can be obtained.
2 1y+25(50-y)=900, 4y=350, irrelevant.
From this, we can choose two schemes: one is to buy 25 TV sets in A and B respectively; The second is to buy 35 A TV and 15 C TV.
(2) If you choose scheme ① in (1), you can make a profit.
150× 25+250×15 = 8750 (yuan)
If you choose scheme ② in (1), you can make a profit.
150× 35+250×15 = 9000 (yuan)
9000 & gt Therefore, in order to get the maximum profit, choose the second scheme.