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context: the article is talking about how to reduce the cost of transport by rocket.
it states that "it currently costs approximately $10,000 per pound to put payloads in orbit, more than their value if they were made of gold."

later it says:

"Efforts are underway to bring down rocket costs through the use of reusable launch vehicles, but costs will have to come down by a factor of at least 100 in order to develop a mass market."

now I understand the phrase "by a factor of" means "a degree of", but I have trouble in understanding the following number 100.

what does it mean: 100 of what? dollars? pounds? percent?

or, a factor of 100 is a particular unit?

here is the link:

http://www.maglev2000.com/works/how-01-c.html
Comments  
The mathematical term 'factor' means the numbers which can be multiplied together to reach the product; the number 12 has 8 different possible integers as factors (12 x 1; 6 x 2; 4 x 3).

$10,000 = 100 x $100. In this mathematical equation, '100' and '$100' are factors of '$10,000.

The costs will have to come down to $100 per pound.
Factor is used for both division and multiplication.
In this case it's division that's involved.
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still not very clear.

the original text says "by a factor of 100" not "at a factor of 100".

how do we know it must come down to $100 not just $100 less?
Review your English math: factor isn't used in subtraction or addition, only in multiplication and division, which you have been told already.

>the original text says "by a factor of 100" not "at a factor of 100"

The original text is right. Your version isn't good English.
Pchuangstill not very clear.

the original text says "by a factor of 100" not "at a factor of 100".

how do we know it must come down to $100 not just $100 less?
Currently, these products are sold for $4000. As part of our promotion, they will be reduced by $100. -- It will come down by $100.

Currently, these products are sold for $4000, but due to some incredible technological innovation, prices will soon come down by a factor of 10. -- They will be $4000/10 or $400 each.

Currently, these products are sold for $4000. But until they come down by a factor of 100, the likelihood of most Americans having one their home is slim. -- They will have to be $4000/100 or $40 each.
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now, that is a great explanation!

thank you all!