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3 years ago

After a shipwreck, Sam is stranded on a desert island. He needs to build a shelter, so he

Mathematics

1 answer:

Llana [10]3 years ago

7 0

Answer:

There kind of needs to be more information. We don't have any other information other than the backstory. You're gonna need to elaborate.

Step-by-step explanation:

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Solve the following equations: (a) x^11=13 mod 35 (b) x^5=3 mod 64

tino4ka555 [31]

$x^{11}=13\pmod{35}\implies\begin{cases}x^{11}\equiv13\equiv3\pmod5\\x^{11}\equiv13\equiv6\pmod7\end{cases}$

By Fermat's little theorem, we have

$x^{11}\equiv (x^5)^2x\equiv x^3\equiv3\pmod5$

$x^{11}\equiv x^7x^4\equiv x^5\equiv6\pmod 7$

5 and 7 are both prime, so $\varphi(5)=4$ and $\varphi(7)=6$ . By Euler's theorem, we get

$x^4\equiv1\pmod5\implies x\equiv3^{-1}\equiv2\pmod5$

$x^6\equiv1\pmod7\impleis x\equiv6^{-1}\equiv6\pmod7$

Now we can use the Chinese remainder theorem to solve for $x$ . Start with

$x=2\cdot7+5\cdot6$

Taken mod 5, the second term vanishes and $14\equiv4\pmod5$ . Multiply by the inverse of 4 mod 5 (4), then by 2.

$x=2\cdot7\cdot4\cdot2+5\cdot6$

Taken mod 7, the first term vanishes and $30\equiv2\pmod7$ . Multiply by the inverse of 2 mod 7 (4), then by 6.

$x=2\cdot7\cdot4\cdot2+5\cdot6\cdot4\cdot6$

$\implies x\equiv832\pmod{5\cdot7}\implies\boxed{x\equiv27\pmod{35}}$

$x^5\equiv3\pmod{64}$

We have $\varphi(64)=32$ , so by Euler's theorem,

$x^{32}\equiv1\pmod{64}$

Now, raising both sides of the original congruence to the power of 6 gives

$x^{30}\equiv3^6\equiv729\equiv25\pmod{64}$

Then multiplying both sides by $x^2$ gives

$x^{32}\equiv25x^2\equiv1\pmod{64}$

so that $x^2$ is the inverse of 25 mod 64. To find this inverse, solve for $y$ in $25y\equiv1\pmod{64}$ . Using the Euclidean algorithm, we have

64 = 2*25 + 14

25 = 1*14 + 11

14 = 1*11 + 3

11 = 3*3 + 2

3 = 1*2 + 1

=> 1 = 9*64 - 23*25

so that $(-23)\cdot25\equiv1\pmod{64}\implies y=25^{-1}\equiv-23\equiv41\pmod{64}$ .

So we know

$25x^2\equiv1\pmod{64}\implies x^2\equiv41\pmod{64}$

Squaring both sides of this gives

$x^4\equiv1681\equiv17\pmod{64}$

and multiplying both sides by $x$ tells us

$x^5\equiv17x\equiv3\pmod{64}$

Use the Euclidean algorithm to solve for $x$ .

64 = 3*17 + 13

17 = 1*13 + 4

13 = 3*4 + 1

=> 1 = 4*64 - 15*17

so that $(-15)\cdot17\equiv1\pmod{64}\implies17^{-1}\equiv-15\equiv49\pmod{64}$ , and so $x\equiv147\pmod{64}\implies\boxed{x\equiv19\pmod{64}}$

5 0

3 years ago

15 percent of what number is 12

blagie [28]

12÷15<u /><em />=160
you have to divide 12 by 15 percent to get the missing number

5 0

3 years ago

Read 2 more answers

What compound inequality describes this graph

nadezda [96]

Answer:

0≥x<4

Step-by-step explanation:

first, let's look at this number line.

there is a closed circle at 0 and an open circle at 4. this means that 0 is included (≤ or ≥) and that 4 is not included (< or >).

these are the endpoints, meaning that in this compound inequality, the numbers next to the symbols are 0 and 4.

x is in the middle of this compound inequality.

0 x 4

now, we have to figure out the symbols in between. i wrote out our choices above for each number. the highlighted portion is greater than or equal to 0 and less than 4, so we can write this compound inequality as the following:

0≥x<4

x is greater than or equal to 0, but less than 4

4 0

3 years ago

Solve for x in the equation 2x^2+14x+17=-96

goblinko [34]

$2x^{2}+14x+17=-96 \newline
2x^{2}+14x+113=0 \newline
\Delta = b^{2}-4ac = 14^{2} - 4 \cdot 2 \cdot 113 = -708.$

Since $\Delta$ is negative $\Rightarrow x \notin \mathbb{R}.$

5 0

3 years ago

Q7.

VLD [36.1K]

Answer:

Step-by-step explanation:

Let c = sum of ages of all children.

mean age of all children = c/15 = 7

c = 15 * 7 = 105

The sum of the ages of all children is 105.

Let b = sum of ages of the 9 boys.

mean age of boys = b/9 = 5

b = 9 * 5 = 45

The sum of the ages of the boys is 45.

The sum of the ages of the girls is c - b.

c - b = 105 - 45 = 60

The number of girls is 15 - 9 = 6

mean age of girls = (sum of ages of the girls)/(number of girls) =

= 60/6 = 10

3 0

3 years ago