2. A trapezoid, 2 cm high, the bottom is 3 times that of the upper bottom. When the upper bottom is extended by 2 cm, it becomes a parallelogram. How many centimeters are the upper and lower bottoms of this trapezoid? Solution: If the upper bottom is X and the lower bottom is 3x x+2=3x, then the upper bottom and the lower bottom are 1 and 3cm respectively.
Xiaoming, Xiao Yong and Xiaofeng are playing cards together. Xiao Ming has six cards and Xiao Yong has seven cards. Xiaofeng takes a card from Xiaoming and Xiao Yong at a time and then returns it to them. * * * There are (b) different methods. 13
1The teacher led four boys and five girls to go boating in the park. Now there is only one boat, which can take three people at a time. (1) If the teacher doesn't get on the boat, there are 1 boys and 2 girls on the boat. How many different collocation methods are there? Answer: 40 kinds (2) If the teacher doesn't get on the boat and there are two boys and 1 girl on the boat, how many different collocation methods are there? Answer: 30 kinds (3) If the teacher wants to board the ship, there are 1 boys and 1 girls on board. How many different collocation methods are there? Answer: 20 kinds (4) If the teacher wants to board the ship and there are two students on board, how many different collocation methods are there? A: 36 kinds.
A train has 22 carriages, each carriage is 12m long, and the distance between the two carriages is1m. The speed of this train is 25m/s, how long does it take for it to cross a bridge of 1440m? Answer [22 *12+1* (22-1)+1440] ÷ 25 = 69 (seconds).
6. The barber shop has only 1 barber and three customers, A, B and C, which need 15 minutes, 30 minutes and 10 minutes respectively. According to the order of (c, a, b), the waiting time of three customers can be minimized, and the total waiting time of three customers is (35).
7. There are 120 flowers in the horizontal row and 96 flowers in the vertical row in the garden. If you move these flowers to the factory at most, how many rows can you put every 45 trees? Answer: 120*96÷45=256 (line)
8. It is known that the circumference of an isosceles triangle is one centimeter, the length of the base is 12 centimeter, and the base angle is b degrees. The waist length and the degree of the vertex angle are expressed by a formula. How long is its waist when a=30 cm? Answer: Waist circumference: (a- 12)÷2
Vertex angle: (180-2b); When a = 30cm, waist circumference: (30- 12) ÷ 2 = 9cm.
9. It takes 12 minutes to cut a piece of wood into 4 sections. How many minutes will it take if you cut this piece of wood into 8 pieces? (column calculation)
A:12 ÷ (4-1) * (8-1) = 28 (points).