1 / 8 + 1 / 7 =? 1 / 4 + 4 / 5 =? 1 / 6 + 1 / 4 =? If you want to make a formula, how can you teach me to calculate?

Using the method of general division
a/b+c/d=（ad+bc）/bd

RELATED INFORMATIONS

1. 7, 5, 6, 9, 4 =? 5, 2, 4, 1, 5 =? 8, 6, 2, 3, 2 =? 3 formulas, What I'm talking about is that the results of the three problems have to be calculated all the time. I'm talking about that the first problem is 7, and the second and third problems have to be calculated with the same numerical results
2. A simple method is used to calculate; 2008-2-4-6-8. - 98-1000
3. 2800-2-4-6-8. - 98-100 by simple method
4. How to calculate 2800-2-4-6-8. - 98-100 with a simple method in the fourth grade?
5. 1. A person deposits 1000 yuan in the bank now. If the annual interest rate of the deposit is 5% and the compound interest is calculated, how much money can he get back from the bank in three years?
6. 1. In order to withdraw 1000 yuan from the bank after 5 years, someone asks for the current deposit amount under the condition of compound interest rate of 2%
7. It is expected to withdraw 1000 yuan from the bank at the beginning of each year in five years with an annual interest rate of 10%. How much yuan should be deposited in the bank at the beginning of the period according to compound interest? Please tell us the calculation process At the beginning of the year, how many interest periods is the withdrawal from the bank? If the interest is not calculated, it is five cycles This is one of the review questions of engineering economics for the first class constructor in 2010. The textbook prompts that the standard answer is 3791. I am not sure about the number of interest periods. Generally, it is not calculated by year. This is calculated by the beginning of the year, mainly to determine the number of interest periods
8. 1. Deposit 1000 yuan in the bank, the annual interest rate is 8%, compound interest once a quarter, what is the final value after five years?
9. 1. The principal is 1000 yuan, invest in a fund, annual fixed income is 5% (compound interest) 2. Investment in a fund, annual fixed income 5% (compound interest), someone invested 1000 yuan at the beginning of each year, 10 years in a row, ask after 10 years and interest (it's better to have the process and result, and the idea of solving the problem)
10. If you deposit 1000 yuan into the bank at the beginning of ten years, the interest rate of the bank is 6%. What is the sum of the interest rate after ten years?
11. 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10.100 = how much, how to calculate with the formula
12. What formula is used in the simple calculation of 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 = 15?
13. What is 2 + 4 + 6 + 8 + 10.. + 1000
14. 2+4+6+8+10+12+...+1000
15. 2+4+6+8+.+1000+1002
16. Then 2 + 4 + 6 + 8 +. + 1000 = () Starting from 2, the sum of consecutive n even numbers is 2 + 4 = 6 = 2x3; 2 + 4 + 6 = 12 = 3x4; 2 + 4 + 6 + 8 = 20 = 4x5 Then the sum of N consecutive even numbers should be 2 + 4 + 6 + 8 +. = (). Then 2 + 4 + 6 + 8 +. + 1000 = ()
17. 2+4+6+8.1000 .. .
18. According to calculation, the thickness of 10000 sheets of paper is about 1 meter. Can you calculate the thickness of 1000 sheets of paper, 100 sheets of paper and 10 sheets of paper according to the thickness of 10000 sheets of paper?
19. (1 / 10 + 1 / 100 + 1 / 1000 + 1 / 10000) / (1 / 100 + 1 / 1000) simple calculation
20. Find the rule 0.175 1.8 0.35 0.9 0.7 0.45 () ()