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Scorpion4ik [409]
3 years ago
10

Why does multiple of 3 add up digits trick work?

Mathematics
1 answer:
kherson [118]3 years ago
7 0
You must be referring to the quick way to determine whether a given integer is divisible by 3; that is, 3 divides an integer x whenever the digits of x sum to a multiple of 3.

Suppose x has n\ge1 digits. We can expand it as a sum of the numbers in any given digits place by the corresponding power of 10. For example, if x=2148, we can write

2148=2\times10^3+1\times10^2+4\times10^1+8\times10^0

More generally, if

x=d_{n-1}d_{n-2}\ldots d_1d_0

(where d_i denotes the numeral in the 10^i-th's place), then we have the expansion

x=d_{n-1}10^{n-1}+d_{n-2}10^{n-2}+\cdots+d_110^1+d_0

Notice that for any integer k, we have

10^k-1=\underbrace{99\ldots99}_{k\text{ 9s}}

which is clearly divisible by 3. So from each power of 10 in the expansion of x, we can add and subtract 1, then rearrange the terms of the sum:

x=d_{n-1}10^{n-1}+\cdots+d_110^1+d_0
x=d_{n-1}(10^{n-1}-1+1)+\cdots+d_1(10^1-1+1)+d_0
x=d_{n-1}(10^{n-1}-1)+\cdots+d_1(10^1-1)+(d_{n-1}+\cdots+d_1+d_0)

We know 10^k-1 is divisible by 3, which means the remainder upon dividing x by 3 is just the sum of the digits of x. If this remainder is divisible by 3, then so must be the original number, x.

Back to our previous example: if x=2148, then we have the expansion

2148=2\times10^3+10^2+4\times10+8
2148=2(999+1)+(99+1)+4(9+1)+8
2148=2\times999+99+4\times9+(2+1+4+8)

Dividing through by 3, we get a remainder of 2+1+4+8=15, which is divisible by 3, and so 2148 must also be a multiple of 3.

In case for some reason you're not convinced 15 is a multiple of 3, you can apply the same trick:

15=10+5
15=9+1+5

Dividing through by 3 leaves a remainder of 1+5=6, which is also a multiple of 3, so that 15 must be, too.
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Given f (X) = 4x +6 find f (x) = 54
Nikitich [7]

Answer:

x = 12

Step-by-step explanation:

Step 1: Define

f(x) = 4x + 6

f(x) = 54

Step 2: Substitute variables

54 = 4x + 6

Step 3: Solve for <em>x</em>

<u>Subtract 6 on both sides:</u> 48 = 4x

<u>Divide both sides by 4:</u> 12 = x

Step 4: Check

<em>Plug in x to verify it is a solution.</em>

f(12) = 4(12) + 6

f(12) = 48 + 6

f(12) = 54

3 0
3 years ago
Read 2 more answers
The antibiotic clarithromycin is eliminated from the body according to the formula A(t) = 500e−0.1386t, where A is the amount re
PolarNik [594]

Answer:

Time(t) = 11.61 hours (Rounded to two decimal place)

Step-by-step explanation:

Given: The antibiotic  clarithromycin is eliminated from the body according to the formula:

A(t) = 500e^{-0.1386t}                 ......[1]

where;

A - Amount remaining in the body(in milligram)

t - time in hours after the drug reaches peak concentration.

Given: Amount of drug in the body is reduced to 100 milligrams.

then,

Substitute the value of A = 100 milligrams in [1] we get;

100= 500e^{-0.1386t}

Divide both sides by 500 we get;

\frac{100}{500}=\frac{ 500e^{-0.1386t}}{500}

Simplify:

\frac{1}{5} = e^{-0.1386t}

Taking logarithm both sides with base e, then we have;

\log_e (\frac{1}{5})= \log_e (e^{-0.1386t})

\log_e (\frac{1}{5})=-0.1386t         [ Using \log_e e^a =a ]

or

\log_e (0.2)=-0.1386t

-1.6094379124341 = -0.1386t

 [using value of \log_e (0.2) = -1.6094379124341 ]

then;

t = \frac{-1.6094379124341}{-0.1386}

Simplify:

t ≈11.61 hours.

Therefore, the time 11.61 hours(Rounded two decimal place) will pass before the amount of drug in the body is reduced to 100 milligrams


6 0
2 years ago
Please I need help with this?​
Alik [6]

9514 1404 393

Answer:

  (a)  positive and increasing

Step-by-step explanation:

Point c is on the x-axis, and point d is above it. The curve between points c and d is positive and increasing.

3 0
3 years ago
Find the zeros of the function y = x^2-1.
kumpel [21]

Answer:

Step-by-step explanation:

x^2-1=0

Add  1 to both sides of the equation.

x^2= 1

Take the square root of both sides of the equation to eliminate the exponent on the left side.

x = ± √ 1

Any root of  1  is  x = ± 1

First, use the positive value of the  ±

to find the first solution.

x= 1

Next, use the negative value of the  ±

to find the second solution.

x = − 1

The complete solution is the result of both the positive and negative portions of the solution.

x = 1 , − 1

4 0
3 years ago
Read 2 more answers
2.) Damian types 110 words in 5 minutes. Howard types 208 words
jekas [21]

Answer:

Step-by-step explanation:

First, divide each persons rate by the number of minutes they typed their words in .

you end up with:

Damian: 55 seconds

Howard: 26 seconds

This tells us that Howard was least and <u>Damian was greater. </u>

Hope this helps :)

6 0
2 years ago
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