1.3.8.15 what is the 10th number?

1.3.8.15 what is the 10th number?

Ninety-nine
3=2^2-1
8=3^2-1
The tenth number is 10 ^ 2-1 = 99
1+3=4=2^2
1+8=9=3^2
1+15=16=4^2
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1+99=100=10^2
Write a random number, such as 341. There is a rule,
1 3 8 15 27 46 79 129 210 341
2 5 7 12 19 31 50 81 131
So digital reasoning without options is meaningless!
The number sequence is the nth power of 2 minus 1, and the 10th number is the 10th power of 2 minus 1 to 1023.
From the second number, it is consistent with the law
The second number is 2 & sup2; - 1 = 3
The third number is 3 & sup2; - 1 = 8
The fourth number is 4 & sup2; - 1 = 15
…………
The nth number is n & sup2; - 1
The tenth number is 10 & sup2; - 1 = 99
The rule is n ^ 2-1
10^2-1=99
From a to B, it takes four hours for a car and five hours for a bus. The speed ratio of a bus to a car is ()
It is known that the radius of a small circle is 2cm, the radius of a large circle is 3cm, the perimeter ratio of a large circle to a small circle is (): (), and the area ratio of a large circle to a small circle is (): ()
emergency
From a to B, it takes 4 hours for a car and 5 hours for a bus. The speed ratio of a bus to a car is 1 / 4:1 / 5 = 5:4;
It is known that the radius of a small circle is 2cm, the radius of a large circle is 3cm, the perimeter ratio of a large circle to a small circle is (2): (3), and the area ratio of a large circle to a small circle is (4): (9)
(1) Suppose the car speed is x, the bus speed is y, the formula is 4x = 5Y, and the speed ratio of bus to trolley is 5:4
(2) The perimeter ratio is 3:2 and the area ratio is 9:4
Can 49 + 99 * 49 be easily calculated?
How did 1 come from?
How did you get the "1"?
The process is like this
49＋1*49
49+99*49
=49*(99+1）
=49*100
=4900
this is it
adopt
Let me tell you in detail how "1" comes from
49+49x99
=49x1+49x99
=49x(1+99)
=49x100
=4900
Do you understand how "1" comes from?
49=1*49
49x（1+99）
=4900
No, I can responsibly say that they read it wrong. Question: I don't think so, after all, it's not the same factor.
A gives 1 / 6 to B and B gives 20% to A. now each has 120
A and B have some money. A gives 1 / 6 to B, and B gives 20% to A. now each has 120. How much did a and B have
It's going to involve you
120÷（1-20%）=150
120×2-150=90
A original: 90 (1-1 / 6) = 108
B: 240-108 = 132
The distance traveled by a large truck is one fourth more than that of a small car, while the travel time of a small car is one tenth more than that of a large truck. What is the speed ratio of a large truck to a small car
A quarter and a tenth,
Set V1, T1, S1 for large trucks
Car V2, T2, S2
S1=5/4S2
V1t1=5/4V2t2
V1t1=5/4V2*11/10t1
V1=11/8V2
V1/V2 = 11/8
What is the most convenient calculation method of mathematics problem (1) 1 + 2 + 3 +. + 1999 + 2000 (2) 1 + 3 + 5.197 + 199?
Simple arithmetic sequence summation
1+2+3+… +1999+2000=（1+2000）*2000/2=2001000
1+3+5+… +197+199=(1+199)*100/2=10000
1 in 2-8 to 7 in 8
1 in 2-8 to 7 in 8
=2-(1/8+7/8)
=2-1
=1
Original question = 2 - (1 / 8 + 7 / 8) = 2-1 = 1
It's one
Big trucks travel 50 kilometers per hour, and small cars travel 60 kilometers per hour. They start from two places 660 kilometers apart at the same time, and go on the contrary. After a few hours, the two cars meet
Meeting Time
660 ÷ (50 + 60) = 6 hours
660 ÷ (50 + 60) = 6 hours
After six hours, the two cars met
I wish you progress in your study and hope you will adopt it~~
Do not understand welcome to ask~~
Simple 1 × 2 + 2 × 3 + 3 × 4 + +99×100
1×2+2×3+3×4+………… +99 × 100 by the way, it's easy to listen to
1×2+2×3+3×4+… +99×100
=（12+1）+（22+2）+（32+3）+… +（992+99）
=（12+22+32+… +992）+（1+2+3+… +99）
= 99(99+1)(2×99+1)/6+ 99×(99+1)/2
=333300
1： Decomposition method
1 × 2 + 2 × 3 + 3 × 4 + The + 99 × 100 is decomposed into 1 × (1 + 1) + 2 × (2 + 1) + 3 × (3 + 1) + The expansion of + 99 × (99 + 1) is: the square of 1 + the square of 1 + 2 + the square of 2 + 3 + 3 + Square of + 99 + 99, after finishing, we can get square of 1 + square of 2 + square of 3 + Square of + 99 + 1 + 2 + 3 + 4 + 99, where the square summation formula of continuous natural numbers starting from 1 is: (2n + 1) (n + 1) n △ 6
2、 Find out
1： Decomposition method
1 × 2 + 2 × 3 + 3 × 4 + The + 99 × 100 is decomposed into 1 × (1 + 1) + 2 × (2 + 1) + 3 × (3 + 1) + The expansion of + 99 × (99 + 1) is: the square of 1 + the square of 1 + 2 + the square of 2 + 3 + 3 + Square of + 99 + 99, after finishing, we can get square of 1 + square of 2 + square of 3 + Square of + 99 + 1 + 2 + 3 + 4 + 99, where the square summation formula of continuous natural numbers starting from 1 is: (2n + 1) (n + 1) n △ 6
2、 Law finding method
1×2=1×2×3÷3
1×2+2×3=2×3×4÷3
1×2+2×3+3×4=3×4×5÷3
1×2＋2×3＋3×4＋…… + 99 × 100 = 99 × 100 × 101 △ 3 = 333300
The general formula is (n + 1) n = n ^ 2 + n
Then 1 ^ 2 + 2 ^ 2 + 3 ^ 2 +... + n ^ 2 = n (n + 1) (2n + 1) / 6. This is a formula, which is necessary to solve this problem
The original formula = 1 * (1 + 1) + 2 * (2 + 1) + 3 (3 + 1) + 4 (4 + 1) + +98(98+1)+99(99+1)
=(1^2+1)+(2^2+2)+(3^2+3)+(4^2+4)+…… +(98^2+98)+(99^2+99)
How to solve the problem that minus 5 / 8 x equals 15 will be explained by friends
Are you sure you have the right number? Should it be minus five eighths x = 15? Or is there something left in front of minus? - 5 / 8x = 15 multiply both sides by - 8 / 5 to get x = - 24?
Minus five eighths x equals 15?
15 / 8 minus (1 / 3 plus 0.75) please help with the formula and answer
15 is 120 out of eight, x minus five out of eight is 12 out of eight, so x is 125 out of eight