3 / 7 of a number is 21. What is 1 / 7 of this number?

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• 1. 5 / 12, 5 / 8, 2 / 5, 1 / 15, 11 / 40, 7 / 24 divide these six numbers into three groups, so that the sum of two fractions in each group is equal
• 2. A fraction, the numerator plus 1, is 3 / 5, and the denominator minus 1, is 4 / 7 You can't use equations to list the formulas. It's a problem for primary school students
• 3. 100 points
• 4. A resistor is connected in series with a 3-ohm resistor and then connected in the original circuit. If the current passing through becomes 4 / 5 of the original current, what is the resistance value of this resistor?
• 5. 21:56 = 3 / 8 = 12 △ () = ()
• 6. Write the simple calculation process (1) 1 and 7 / 3 * 5 / 2 + 2 and 7 / 4 * 5 / 2 + 2 / 5 (2) 2.5 * 12.5 * 3.2 (3) (8 / 2) (3) (7 / 8-7 / 12) * 2.4/1 / 7 (4) 805 * 101-805
• 7. 3 of 7 parts plus 3.6 minus 1 of 7 parts plus 6.4 (simple calculation)
• 8. One in three, one in two minus one in two, one in four equals zero with brackets
• 9. 3.14 times 1 and 3 / 8 plus 0.314 times 25 / 4 minus 31.4 times 0.2
• 10. 11 out of 8 minus 11 out of 15
• 11. 6 out of 7 plus 2 out of 9 minus 1 out of 21
• 12. 9 x (x is an integer), when x equals () the number equals 0
• 13. How to solve that 2x + 30x equals 13.8
• 14. (78 + 91 + 80 + 79 + x) / 4 + 6 = x what does x equal
• 15. A simple calculation method for 1 + 3 + 6 + 10 + 15 + 21 + 28. + 4950 + 5050
• 16. How many years is 1755 days
• 17. A few fourths plus two sevenths is two fifths What's more, 7 out of 15 minus 3 is equal to 2 out of 15, 5 out of 12 minus 18 is equal to 11 out of 36, and 5 out of 3 minus 12 is equal to 11 out of 60?
• 18. Solving the equation: 7 divided by x equals 14 / 15 How to change division sign into Chinese character
• 19. Write two division formulas according to 3 / 7 × 2 / 5 = 6 / 35 ♢ ﹥ 9826; = 3 / 4 × 1 / 9 = ﹥ 9826
• 20. If a number less than 200 is divided by 11 to 8 and 13 to 10, then the number is______ ．