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Standard arithmetic: + - * / %. Integer / truncates: 7 / 3 is 2. Float division when at least one operand is a float: 7.0 / 3 is 2.333….

val a = 17
val b = 5
println(a + b)        // 22
println(a / b)        // 3   (integer)
println(a.toDouble() / b) // 3.4
println(a % b)         // 2

Conversion is explicit — no implicit widening:

val i: Int = 5
val d: Double = i.toDouble()
val s: String = i.toString()

Kotlin numbers don't auto-promote. Use .toLong(), .toDouble(), etc. The kotlin.math package has sqrt, pow, abs, max, min, etc. — many also exist as extension methods on the numeric types.