18÷(5+4)×8
=2×8
=16km
There are five barrels of oil with the same weight. If you take out 15kg from each barrel, the remaining oil in five barrels is exactly equal to the original two barrels. It turns out that a barrel of oil weighs 25 kilograms.
15×5÷(5-2)
=75÷3
=25 kg
3. The cement factory originally planned to complete a task in 12 days, but it finished the task in 10 days because it produced 4.8 tons more cement every day, and originally planned to produce 24 tons of cement every day.
4.8× 10÷( 12- 10)
=48÷2
=24 tons
4. bright primary school held a math knowledge contest with 20 questions. Answer a question correctly and get 5 points; If the answer is wrong, deduct 3 points; If you don't answer, 0 points. Xiao Li scored 79 points, and she got it right (7), wrong (2), and left (1) unanswered.
5×20-79=2 1.
2 1=2×(5+3)×2+5× 1
10-2- 1=7
5.a train is 240 meters long and travels 20 meters per second, and B train is 264 meters long and travels 16 meters per second. It takes (65,438+04) seconds for the two cars to move in opposite directions, from the moment they meet to the moment they separate.
(240+264)÷(20+ 16)
=504÷36
= 14 second
6. Every 50-cent pencil is sold in the school store, and few people buy it. But after the price reduction, all the pencils in stock were sold out at once, and * * * sold for 3 1.93 yuan. There are (65,438+003) pencils in stock, and each pencil is reduced by (0.65,438+09) yuan.
3 1.93=0.3 1× 103
0.5-0.3 1=0. 19 yuan
There are the same number of black balls and white balls in the box. Take out eight black balls and five white balls at a time. After taking it out several times, the black ball disappeared, leaving 12 white ball. I took the exam four times. There are (64) balls in the box.
12/5÷( 1/5- 1/8)
= 12/5÷3/40
=32
32×2=64
32÷8=4 times
8. Miss Wang has a box of pencils, such as 1 two students use pencils, two students use pencils, three students use pencils, four students use pencils and five students use pencils. There are at least 59 pencils in this box.
The least common multiple of 2, 3, 4 and 5 is 60.
60- 1=59 pieces
9. A road construction team undertook the task of building roads. The original plan was to repair 720 meters a day, but the actual repair was 800 meters a day, so that the actual repair difference 1200 meters can be completed three days in advance. The total length of this highway is (10800) meters.
(3- 1200/800)÷( 1/720- 1/800)
= 1.5÷ 1/7200
=10800m
10. Football teams A, B, C, D and E play a single round robin match (one game for every two teams). In each game, the winning team scored 3 points, the losing team scored 0 points, and each team scored 1 point. If the total scores of Team A, Team B, Team C and Team D are 1, 4, 7 and 8 respectively.
A 0 wins 1 draw and 3 losses
B 1 win 1 draw and 2 losses
C 2 wins 1 draws 1 loses
D 2 wins, 2 draws and 0 losses
E 1 win, 3 draw and 0 loss
1 1. If Xiaoming walks 50 meters every minute from home to school, it's just class time. If you walk 60 meters per minute, there are still 2 minutes before class, and it is (600) meters for Xiao Ming to go from home to school.
2÷( 1/50- 1/60)
=2÷ 1/300
=600 meters
12. Grandma Wang has 40 eggs and a chicken that lays an egg every day. If Grandma Wang eats three eggs every day, she can eat them for (20) days.
40(3- 1)= 20 days
13. In the following equation, the same letters represent the same numbers, and different letters represent different numbers. If abcd-dcba=x997, then x=( 2).
X+7 is a multiple of 9 and x=2.
14. Wang, a professional pig farmer, said, "If you sell 75 pigs, the feed can last for 20 days. If you buy 100 pigs, the feed can only last 15 days. " Uncle Wang keeps (600) pigs.
(20×75+ 15× 100)÷(20- 15)
=3000÷5
=600 heads