1/2+1/6+1/12+1/20+1/30+1/42+1/56=? 5/（1+6）+5/（6+11）+5/（11+16）+…… +5/（76+81）=? （1+2+3+4+5+6+7+6+5+4+3+2+1）/（777777*777777）=? Published by Yanbian Education Press this year, on page 27 I am in college, this kind of problem should have been done in high school, but I forgot it early, it really affects the image of college students in the little cousin's heart!

1/2+1/6+1/12+1/20+1/30+1/42+1/56=? 5/（1+6）+5/（6+11）+5/（11+16）+…… +5/（76+81）=? （1+2+3+4+5+6+7+6+5+4+3+2+1）/（777777*777777）=? Published by Yanbian Education Press this year, on page 27 I am in college, this kind of problem should have been done in high school, but I forgot it early, it really affects the image of college students in the little cousin's heart!

（1）.1/2+1/6+1/12+1/20+1/30+1/42+1/56
=1/2+1/2*1/3+1/3*1/4+...+1/7*1/8
=1/2+(1/2-1/3)+(1/3-1/4)+（1/4-1/5）+（1/5-1/6）+（1/6-1/7）+（1/7-1/8）
=1/2+1/2-1/8
=7/8
（2）.5/（1+6）+5/（6+11）+5/（11+16）+…… +5/（76+81）
Did you copy it wrong
5/（1*6）+5/（6*11）+5/（11*16）+…… +5/（76*81）
=1-1/6+1/6-1/11+...+1/76-1/81
=1-1/81
=80/81
The method is the same as above
(3).(1+2+3+4+5+6+7+6+5+4+3+2+1）/（777777*777777）
=7*7/(777777*777777)
=1*1/(111111*111111)
=1/（111111*111111）
11*11=121
111*111=12321
1111*1111=1234321
...
111111*111111=12345654321

3. There are 24 cars and motorcycles. Cars have 4 wheels and motorcycles have 2 wheels. These cars have 78 wheels. How many motorcycles are there?
4. Eight cases of apples were delivered from the store, each of which has the same weight. After taking 15 kg from each case, the remaining weight is exactly equal to the original weight of two cases. How many kg and how many kg of apples did each case weigh?
7. A grain store has two warehouses. The number of grain bags in the first warehouse is three times that in the second warehouse. If 78 bags are transferred from the first warehouse to the second warehouse, the number of grain bags in the two warehouses is exactly the same. How many bags of original grain are there in the two warehouses
Note: I hope the simpler the answer is, the better. But there must be basis

3. (24 * 4-78) / (4-2) = 9 (vehicles)
4. 15 * 8 △ 6 = 20 (kg)
7. 78 * 2 ÷ (3-1) = 78 (bag)
78 * 3 = 234 (bag)

This is a summer homework application!
A car factory produced 89 cars on Monday, 74 on Tuesday, 81 on Friday and 85 on Saturday. It was 7 on Wednesday and 8 on Thursday. What's the requirement? Besides, the average quantity is 79. It's going to start school soon,
What's the formula

For the single digit of Wednesday: the single digit of average 79 is 9 * 6 = 54, and the single digit is 4, so the sum of single digits from Monday to Saturday is 9 + 4 + 1 + 5 + X + 8 = 27 + X, and the single digit is 4, so x = 7, so the sum of single digits from Monday to Saturday is 77
For the tens on Thursday: 89 + 74 + 81 + 85 + 77 + y = 79 * 6, the solution is y = 68