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Q: A: ### Quick Answer

**The number 90 is spelled "ninety."** It is formed from its base of nine followed by a -ty which signifies that the number is followed by a tens placeholder.

The number 90 is often misspelled because many people drop the "e" and leave the word as "ninty."

Numbers between 20 and 100 that are multiples of 10 are spelled from a form of the base number followed by the -ty: twenty, thirty, forty, fifty, sixty, seventy, eighty and ninety. For the numbers between them, simply append the spelled number in the ones place to the spelled number in the tens place. For example, to spell 47, simply add "seven" to the end of the spelled number forty to get "forty-seven."

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- Q:
## Is 29 a prime number?

A:

Full Answer >**Twenty-nine is a prime number, as its only divisors are 1 and 29.**A prime number is defined as a whole number that is greater than 1 and is not evenly divisible by any other numbers except 1 and itself.Filed Under: - Q:
## Why is 11 not pronounced as "onety-one"?

A:

Full Answer >**While "onety-one" or "oneteen" would seem to make sense as pronunciations for the number 11, the origin of the word "eleven" is the Old English word "endleofan," literally "one left" (over 10).**How words are pronounced as of 2014 is influenced by how they were pronounced in the past.Filed Under: - Q:
## What is index form in mathematics?

A:

Full Answer >**When a number is expressed with exponents, or one number to a power of another, it is considered to be in index form.**For example, 27 can be written in index form as 3^3. This is because 27 is 3x3x3 or 3^3.Filed Under: - Q:
## What prefix is used for the number "9"?

A:

Full Answer >**The most common prefix for the number nine is "nona-", such as in the word "nonagon," which describes a polygon with nine sides, and "nonagenarian," a person in his 90s.**A less commonly used prefix is "nove-," as in "novennial," which is an event that occurs every nine years.Filed Under:

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