90 (number)

90 (Somali: sagaashan) is a natural number in the numerical system. It follows 89 and precedes 91. In base ten, 90 is composed of two digits: 9 and 0, meaning nine tens and zero units.

The number 90 is a composite number, meaning it has divisors other than 1 and itself. Its prime factorization is 2 × 3 × 3 × 5, or 2 × 3² × 5. It is also an even number because it is divisible by 2.

Mathematical properties

The divisors of 90 are 1, 2, 3, 5, 6, 9, 10, 15, 18, 30, 45, and 90 — a total of 12 divisors. The sum of its divisors excluding 90 itself (1+2+3+5+6+9+10+15+18+30+45) exceeds 90, so 90 is classified as an abundant number. It is also divisible by 9, since the sum of its digits (9+0=9) equals 9.

Geometry

A 90-degree angle is a right angle. It is fundamental to Euclidean geometry: two lines intersecting at 90 degrees form a perpendicular angle. A 90-degree rotation around a point equals a quarter turn. Additionally, one of the angles in a right triangle is 90 degrees, while the sum of the other two is also 90 degrees.

Everyday uses

90 appears in many measurements: a standard association football match lasts 90 minutes (two halves of 45 minutes each). The percentage 90 is used to measure levels of success or achievement. The 90th anniversary marks an important historical milestone.

Names in languages

In Somali, 90 is "sagaashan," derived from "sagaal" (nine) and the tens system. This naming pattern follows that of other numbers: siddeetan (eighty), toddobaatan (seventy). In Arabic script, 90 is written as ٩٠, while Roman numerals represent 90 as XC.