# 2019 Top Ten of Polemic for Mathematics

30,000
30,000 is the natural number that comes after 29,999 and before 30,001
Interquartile range
In descriptive statistics, the interquartile range (IQR) is a measure of statistical dispersion, which is the spread of the data. The IQR may also be called the midspread, middle 50%, or H‑spread. It is defined as the difference between the 75th and 25th percentiles of the data. To calculate the IQR, the data set is divided into quartiles, or four rank-ordered even parts via linear interpolation. These quartiles are denoted by Q1, Q2, and Q3. The lower quartile corresponds with the 25th percentile and
Right triangle
A right triangle or right-angled triangle (British), or more formally an orthogonal triangle, is a triangle in which one angle is a right angle. The relation between the sides and other angles of the right triangle is the basis for trigonometry
Isosceles triangle
In geometry, an isosceles triangle is a triangle that has two sides of equal length. Sometimes it is specified as having exactly two sides of equal length, and sometimes as having at least two sides of equal length, the latter version thus including the equilateral triangle as a special case. Examples of isosceles triangles include the isosceles right triangle, the golden triangle, and the faces of bipyramids and certain Catalan solids
20 (number)
20 is the natural number following 19 and preceding 21. A group of twenty units may also be referred to as a score
1,000,000,000
1,000,000,000 is the natural number following 999,999,999 and preceding 1,000,000,001. With a number, "billion" can be abbreviated as b or bn
Hecto-
Hecto is a decimal unit prefix in the metric system denoting a factor of one hundred. It was adopted as a multiplier in 1795, and comes from the Greek ἑκατόν hekatón, meaning "hundred". In 19th century English it was sometimes spelled hecato, in line with a puristic opinion by Thomas Young. Its unit symbol as an SI prefix in the International System of Units (SI) is the lower case letter h
Pre-algebra
Pre-algebra is a common name for a course in middle school mathematics. In the United States, pre-algebra is usually taught in the 7th grade or 8th grade. The objective of it is to prepare students for the study of algebra. Usually algebra is taught in the 8th and 9th grade
25 (number)
25 (twenty-five) is the natural number following 24 and preceding 26
Parallelogram
In Euclidean geometry, a parallelogram is a simple (non-self-intersecting) quadrilateral with two pairs of parallel sides. The opposite or facing sides of a parallelogram are of equal length and the opposite angles of a parallelogram are of equal measure. The congruence of opposite sides and opposite angles is a direct consequence of the Euclidean parallel postulate and neither condition can be proven without appealing to the Euclidean parallel postulate or one of its equivalent formulations