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Elan Coil [88]
3 years ago
9

If 7x - 4y = 23 and x + y = 8, what is the value of x?

Mathematics
2 answers:
Margaret [11]3 years ago
8 0

Answer:

x=5

Step-by-step explanation:

7x - 4y = 23 and x + y = 8

Multiply the second equation by 4

4x + 4y = 32

Add this to the first equation

7x - 4y = 23

4x + 4y = 32

------------------------

11x    = 55

Divide each side by 11

11x/11 = 55/11

x = 5

QveST [7]3 years ago
5 0

Answer:

\huge\boxed{x=5}

Step-by-step explanation:

\left\{\begin{array}{ccc}7x-4y=23\\x+y=8&|\text{subtract}\ x\ \text{from both sides}\end{array}\right\\\left\{\begin{array}{ccc}7x-4y=23&(1)\\y=8-x&(2)\end{array}\right\\\\\text{substitute (2) to (1):}\\\\7x-4(8-x)=23\qquad|\text{use the distributive property}\\\\7x+(-4)(8)+(-4)(-x)=23\\\\7x-32+4x=23\qquad|\text{combine like terms}\\\\(7x+4x)-32=23\qquad|\text{add 32 to both sides}\\\\11x-32+32=23+32\\\\11x=55\qquad|\text{divide both sides by 11}\\\\\dfrac{11x}{11}=\dfrac{55}{11}\\\\x=5

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Step-by-step explanation:

For each women, there are only two possible outcomes. Either they visit their doctors for a physical examination at least once in two years, or they do not. The probability of a woman visiting their doctor at least once in this period is independent of any other women. This means that we use the binomial probability distribution to solve this question.

Binomial probability distribution

The binomial probability is the probability of exactly x successes on n repeated trials, and X can only have two outcomes.

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In which C_{n,x} is the number of different combinations of x objects from a set of n elements, given by the following formula.

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And p is the probability of X happening.

70% of adult women visit their doctors for a physical examination at least once in two years.

This means that p = 0.7

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This means that n = 20

(a) Fewer than 14 of them have had a physical examination in the past two years.

This is:

P(X < 14) = 1 - P(X \geq 14)

In which

P(X \geq 14) = P(X = 14) + P(X = 15) + P(X = 16) + P(X = 17) + P(X = 18) + P(X = 19) + P(X = 20)

P(X = x) = C_{n,x}.p^{x}.(1-p)^{n-x}

P(X = 14) = C_{20,14}.(0.7)^{14}.(0.3)^{6} = 0.1916

P(X = 15) = C_{20,15}.(0.7)^{15}.(0.3)^{5} = 0.1789

P(X = 16) = C_{20,16}.(0.7)^{16}.(0.3)^{4} = 0.1304

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