Twice as many? 3/4 as many? How to interpret?

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Discussion Overview

The discussion revolves around how to algebraically express phrases like "twice as many x as z" and "3/4 as many x as z." Participants explore the implications of these phrases in mathematical terms, including their application in examples involving quantities like apples and oranges. The conversation includes both theoretical interpretations and practical examples.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Homework-related

Main Points Raised

  • Some participants propose that "twice as many x as z" can be expressed as x = 2z, indicating that for every unit of z, there are two units of x.
  • Others suggest that the phrase could also be interpreted as 2x = z, leading to confusion about the correct formulation.
  • One participant provides an example involving apples and oranges, stating that if there are twice as many apples as oranges, then y = 2x, where y represents oranges and x represents apples.
  • Another participant emphasizes the importance of understanding ratios, stating that "twice as many x as z" implies a ratio of x:z as 2:1, leading to the conclusion that x = 2z.
  • Some participants express uncertainty about the clarity of these statements and whether they are ambiguous.
  • One participant shares a personal experience of struggling with math homework, indicating a potential emotional aspect to the discussion.

Areas of Agreement / Disagreement

There is no consensus on the correct algebraic representation of the phrases discussed. Multiple interpretations exist, and participants express differing views on the clarity and correctness of the statements.

Contextual Notes

Participants highlight the potential ambiguity in the phrasing of the problems and the importance of defining variables clearly. There is also an acknowledgment of the emotional challenges faced when engaging with mathematical concepts for extended periods.

Vay
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How do you write "twice as many x as z" algebraically?

Is this 2x=z or x=2z? How do you know?

How about "3/4 as many x as z" algebraically?

Is this (3/4)x=z or z=(3/4)x? How do you know?

An applied example:
There are twice as many apples as there are oranges, so does this mean for each orange there are 2 apples, so that if apples=x and oranges=y, then y=2x; 2y=4x, and etc?

Are these statements ambiguous to you?
 
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How do you write "twice as many x as z" algebraically?
Is this 2x=z or x=2z?

x = 2z

How do you know?

There's no trick to it; all of the information is right there in the expression. It says that you need 2 of z to equal 1 of x, hence: x = 2z.
 
Vay said:
How do you write "twice as many x as z" algebraically?

Is this 2x=z or x=2z? How do you know?
x = 2z

An equivalent problem is "x is twice as big as z." It might help to look at numbers. 50 is twice as big as 25. Would you write an equation expressing this relationship as
a) 50 = 2*25
or
b)2*50 = 25?
Vay said:
How about "3/4 as many x as z" algebraically?
x = (3/4)y
Vay said:
Is this (3/4)x=z or z=(3/4)x? How do you know?

An applied example:
There are twice as many apples as there are oranges, so does this mean for each orange there are 2 apples, so that if apples=x and oranges=y, then y=2x; 2y=4x, and etc?

Are these statements ambiguous to you?
I would not let apples = x and oranges = y. These variables should represent the number of apples or oranges.

As far as translating to equations, see what I said at the beginning of this post.
 
I don't know what has gotten to me, sometimes I just can't get something. It must be doing my math homework for 6 hours straight... I can't think straight anymore. Anyone else have similar experience? Or it must be something I ate...
 
Vay said:
How do you write "twice as many x as z" algebraically?

I usually try to think of this in terms of ratios. The phrase "twice as many x as z" gives you an equality of ratios, x:z is 2:1. Assuming z isn't zero, we can rewrite this using fractions as \frac{x}{z} = 2 so x = 2z.
 

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