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weeeeeb [17]
3 years ago
9

-x+7y=5,-4x+y=-7 System of equations substitution

Mathematics
1 answer:
Leno4ka [110]3 years ago
5 0

Answer:

<h2>x = 2, y = 1 → (2, 1)</h2>

Step-by-step explanation:

\left\{\begin{array}{ccc}-x+7y=5\\-4x+y=-7&\text{add}\ 4x\ \text{to both sides}\end{array}\right\\\\\left\{\begin{array}{ccc}-x+7y=5&(1)\\y=4x-7&(2)\end{array}\right\qquad\text{subtritute (2) to (1)}\\\\-x+7(4x-7)=5\qquad\text{use the distributive property}\\\\-x+(7)(4x)+(7)(-7)=5\\\\-x+28x-49=5\qquad\text{add 49 to both sides}\\\\-x+28x=5+49\qquad\text{combine like terms}\\\\27x=54\qquad\text{divide both sides by 27}\\\\\boxed{x=2}

\text{Put the value of}\ x\ \text{to (2):}\\\\y=4(2)-7\\\\y=8-7\\\\\boxed{y=1}

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Answer:

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If she reads 25% pages/night, that means reading 0.25(0.70)p pages per night, or 17.5 pages/night.  If 28% p/n, that means 0.28(0.70)p pages/night, or 19.6p pages/night.

How many nights will it take Nora to finish the book if she reads 25% of 7/10 of the book per night?  Without any calculations, we can answer this by "4 nights, since she reads 1/4 of the unread portion of the book per night."

If she reads 28% of 7/10 of the book per night, that will require fewer nights:

First night:  28%

Second night:  28%  

Third night:  28%

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This leaves 16% to read on the final night.

This is one interpretation of what I think is a poorly worded question.

The author of this question might have meant reading 25% of the remaining unread pages per night, which leads to a different answer.

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3 years ago
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