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Lê Quốc Trần Anh Coordinator
19/06/2018 at 03:20
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Three stoplights on different streets each operate on their own independent schedules, as follows: the first stoplight is red 1 minute out of every 2 minutes (1 minute red, then 1 minute green), the second is red 2 minutes out of every 3 minutes (2 minutes red, then 1 minute green) and the third is red 3 minutes out of every 5 minutes (3 minutes red, then 2 minutes green.) At 9:00 am each stoplight turns red. The lights are either red or green (don’t worry about yellow). What time is it when the next 1-minute segment of time in which all three stoplights are red begins? 


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Lê Quốc Trần Anh Coordinator
23/07/2018 at 02:46
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A path crosses a rectangular field on a diagonal. If someone travels across the field on the diagonal, instead of walking along the sides, what is the greatest possible percent reduction in total distance traveled? Express your answer to the nearest whole number.

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    Tôn Thất Khắc Trịnh 23/07/2018 at 06:57

    There is the greatest reduction when the two sides adjacent to the right angle are equal (I mean, a square is technically also a rectangle)
    Using the Pythagorean theorem, we can see that the diagonal is a\(\sqrt{2}\) and the sum of the other sides is 2a
    So the greatest percent of reduction is \(\dfrac{2a-a\sqrt{2}}{2a}=1-\dfrac{\sqrt{2}}{2}\approx29\%\)

    Lê Quốc Trần Anh selected this answer.

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Quoc Tran Anh Le Coordinator
06/08/2018 at 02:34
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An old puzzle asks you to use the numbers 1 through 9 to equal 100.

Example:

123 – 45 – 67 + 89 = 100

OR

1.234 + 98.765 = 100

Can you find one or two more possibilities?

Math Puzzles

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    Lê Anh Duy 06/08/2018 at 06:58

    123 + 4 - 5 + 67 - 89 = 100

    1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 × 9 = 100

    (You only ask two so I have two

    But there are over 200 ways to make 100 by 0 - 9!!!)

    Quoc Tran Anh Le selected this answer.

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Quoc Tran Anh Le Coordinator
01/01/2019 at 12:28
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Vijay gives Sanjay a set of four weights of 1, 3, 8 and 26 grams. When Sanjay places weights on either side of a balance, what is the smallest positive integer number of grams that he cannot measure with this set?

 

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mark zuckerberg
19/03/2017 at 00:45
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what can be the smallest value of a in 6x - a = 5x + 8?

simple equation


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le huyen linh
21/04/2017 at 20:36
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make two number equal  to \(\dfrac{1}{4}\)

of the first number .the two number are 441. find the two number

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    Nguyễn Thị Ý Nhi 21/04/2017 at 20:45

    number first is 4 part so the number first are:441: (4+5) x 4 = 196

    and secound are: 441-196=245... 

    le huyen linh selected this answer.
  • ...
    huyenbloomwinx123 22/04/2017 at 20:29

    Why 4+5?


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Summer Clouds moderators
11/08/2017 at 08:50
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Rayshon has 51 coins consisting of dimes and nickels that total $3.55. How many dimes does he have?

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    Phan Thanh Tinh Coordinator 11/08/2017 at 13:34

    Convert : 1 dime = 10 cents ; 1 nickel = 5 cents ; $3.55 = 355 cents

    Let d and n be the number of dimes and nickels Rayshon has respectively.We have :

    \(\left\{{}\begin{matrix}d+n=51\\10d+5n=355\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}d+n=51\\2d+n=71\end{matrix}\right.\)\(\Rightarrow d=20\)

    So,he has 20 dimes.


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Kaya Renger Coordinator
22/09/2017 at 11:13
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Given x,y satisfy 16x2 - 9y2 \(\ge\) 144 .

Show that : |2x - y + 1| \(\ge\) \(2\sqrt{5}-1\)


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Lê Quốc Trần Anh Coordinator
19/10/2017 at 18:12
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An advertisement states that 4 out of 7 dentists recommend Minty Fresh Mouthwash. If 1421 dentists were surveyed, how many dentists recommended Minty Fresh Mouthwash?

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    Dao Trong Luan Coordinator 19/10/2017 at 18:48

    There are \(\dfrac{1421}{7}\cdot4=812\) dentists recommended Minty Fresh Mouthwash

    Lê Quốc Trần Anh selected this answer.

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Summer Clouds moderators
16/11/2017 at 16:09
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The shape shown is formed by a circle with radius of length r units and two smaller semicircular regions, each with diameter of length r units. What is the perimeter of the shaded portion of the large circle? Express your answer in terms of r and π. 
undefined

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    Phan Thanh Tinh Coordinator 18/11/2017 at 00:19

    The answer is : \(\dfrac{1}{2}\pi r.2+2\pi r.\dfrac{1}{2}=2\pi r\) (units)

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Trigonometric
sin cos tan cot sinh cosh tanh
Lim-log

Combined operations

 

α β γ δ θ σ ∂ ε ω φ ϕ π μ λ Ψ ξ η χ ζ ι κ ν ψ Ω ρ τ υ Γ Δ Λ Φ Π Σ Υ Ξ ϑ Θ ς ϰ
∞ ⊻ ⩞ ⋎ ⋏ ≀ ∪ ⊎ ⋓ ∩ ⋒ ⊔ ⊓ ⨿ ⊗ ⊙ ⊚ ⊛ ⊘ ⊝ ⊕ ⊖ ⊠ ◯ ⊥
⇔ ⇒ ⇐ → ← ↔ ↑ ↓
Operations
+ - ÷ × ≠ = ⊂ ⊃ ⊆ ⊇ ≈ ∈ ∉ ∃ ∄ ≤ ≥ ± ∓ ≠ ∅ ≃ ≅ ≡ ⋮ ⋮̸ ∀
(□) [□] {□} |□|

The type of system

m×n 1×2 1×3 1×4 1×5 1×6
2×1 2×2 2×3 2×4 2×5 2×6
3×1 3×2 3×3 3×4 3×5 3×6
4×1 4×2 4×3 4×4 4×5 4×6
5×1 5×2 5×3 5×4 5×5 5×6
6×1 6×2 6×3 6×4 6×5 6×6

Recipe:

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