15 16 17 18 19 20 six numbers are filled in () of the three sides of the triangle so that the sum of the three numbers on each side is 51

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• 1. (1) 15 of a number is 3.6 less than 1.6 times of 4.5. Find this number. (2) what is the difference between 6 divided by 67 and 6 divided by 67?
• 2. A positive integer plus 32 and 132 is equal to the complete square. How much is the positive integer?
• 3. Clever calculation: how to calculate 1 × 2 + 2 × 3 + 3 × 4 +... + 49 × 50? How to calculate 1 × 2 + 2 × 3 + 3 × 4 +... + 49 × 50
• 4. The sum problem of sequence an = 3 / (2n-11) n belongs to positive integer, and the sum of the first n terms of sequence {an} is Sn, so what is the minimum value of n with Sn ＞ 0 Summation of sequence An = 3 / (2n-11) n is a positive integer, and the sum of the first n terms of the sequence {an} is Sn, so what is the minimum value of n with Sn > 0? In addition to one written out, other clever solutions
• 5. The difference between nine tenths and two fifths subtracts a number to get a quarter. What's the number?
• 6. How many square centimeters is one square decimeter? I've been studying for too long. I'm afraid I'll make a mistake,
• 7. Let x-n (1.5,4) calculate P {x2.5} Let x-n (1.5,4) compute P {X & lt; = 3.5}, P {X & gt; 2.5} a problem about probability
• 8. Given the first n terms of sequence an and Sn = 2n ^ 2 + N, the value of LIM [1 / A1A2 + 1 / a2a3 + 1 / a3a4 +... + 1 / Anan + 1] is
• 9. If the quadratic power of a-ab-12b = 0, and B is not equal to 0, find 2a-b / 2A + B
• 10. Subtract a quarter of a number from the difference between one ninth and two fifths. What is the number? (solve the equation) Subtract a number from the difference between one ninth and two fifths to get a quarter. What's the number? (solving equations)
• 11. Ingenious calculation: (1 / 2 + 1 / 3) - (1 / 3 + 1 / 4) + (1 / 4 + 1 / 5) - (1 / 5-1 / 6) - (1 / 6)+ Clever calculation: （1/2+1/3）-（1/3+1/4）+（1/4+1/5）-（1/5-1/6）-（1/6+1/7）-(1/7+1/8)
• 12. 1 × 2 / 1 + 2 × 3 / 1 + 3 × 4 / 1 + 4 × 5 / 1 + 5 × 6 / 1
• 13. 9.1 + 9.2 + 9.3 + 9.4 + 9.1 + 8.9 + 8.8 (clever calculation)
• 14. Skillful calculation of Mathematics one thousand two hundred and thirteen
• 15. Calculation: (1 -?) 2 (1-1 / 3) 2 (1-1 / 4) 2 ×. (1-1 / 10) 2 What was the result? It's better to explain the calculation method as well Is the square of (1-1 / 2), the square of (1-1 / 3), the square of X (1-1 / 4), and the square of X (1-1 / 10)
• 16. Calculation: (1 + 10 / 1 × 1) + (1 + 10 / 1 × 2) + (1 + 10 / 1 × 3) + +(1 + 10 / 1 × 9) + (1 + 10 / 1 × 10)
• 17. 8 x (- 2) x (- 4) x 1 x (- 3) calculation
• 18. ① Calculation [1 / (1 × 2)] + [1 / (2 × 3)] + [1 / (3 × 4)] + ＋[1／（10×11）]. ② Using the thinking of the above question to calculate: {1 / [a (a + 1)]} + {1 / [(a + 1) (a + 2)]} + {1 / [(a + 2) (a + 3)]} + +The value of {1 / [(a + 2008) (a + 2009)]} + {1 / [(a + 2009) (a + 2010)]}
• 19. Calculation: (3 × 10-5) 2 △ (3 × 10-1) 2
• 20. Calculate 1 + 2 + 2 ^ 2 + 2 ^ 3 + 2 ^ 4 +. 2 ^ 63