90 (number)

90 (ninety) is the natural number preceded by 89 and followed by 91.

← 89 91 → 90
← 90 91 92 93 94 95 96 97 98 99 → List of numbers — Integers 0 10 20 30 40 50 60 70 80 90 →
Cardinal	ninety
Ordinal	90th (ninetieth)
Numeral system	90
Factorization	$2 \cdot 3^2 \cdot 5$
Divisors	1, 2, 3, 5, 6, 9, 10, 15, 18, 30, 45, 90
Roman numeral	XC
Binary	10110102
Octal	1328
Duodecimal	7612
Hexadecimal	5A16

Interstate 90 is a freeway that runs from Washington to Massachusetts.

In mathematics

• Because 90 is the sum of its unitary divisors (excluding itself), it is a unitary perfect number, and because it is equal to the sum of a subset of its divisors, it is a semiperfect number. 90 is a pronic number. But it is also a nontotient. It is a Perrin number, preceded in the sequence by 39, 51, 68.
• In normal space, the interior angles of a square measure 90 degrees each. Also, in a right triangle, the angle opposing the hypotenuse measures 90 degrees, with the other two angles adding up to 90 for a total of 180 degrees.^[1] Thus, an angle measuring 90 degrees is called a right angle.^[2]
• 90 is divisible by the sum of its base 10 digits, thus it is a Harshad number.

In science

• Ninety is the atomic number of thorium, an actinide. As an atomic weight, 90 identifies an isotope of strontium, a by-product of nuclear reactions including fallout. It contaminates milk.
• The latitude of the North Pole and the South Pole are 90 degrees.^{[citation needed]}

In religion

Ninety of the Psalm are credited to Moses; some credit the ninety-first psalm to him as well.

In sports

• Nike Total 90 Apparel is a brand name of football apparel and football equipment from equipment bags to goalkeeper gloves
• Major League baseball bases are 90 feet (27 m) away in distance
• The car number most associated with former NASCAR team owner Junie Donlavey
• The number of minutes in a football (soccer) match.

In Wellness Plans

• P90X is a rigorous work out plan for 90 days with proclaimed incredible results.

See also

Mathematics portal

References

1. ^ http://www.sparknotes.com/testprep/books/newsat/chapter20section4.rhtml
2. ^ Friedman, Erich. What's Special About This Number?