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diff --git a/src/math/rand/example_test.go b/src/math/rand/example_test.go
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+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package rand_test
+
+import (
+	"fmt"
+	"math/rand"
+	"os"
+	"strings"
+	"text/tabwriter"
+)
+
+// These tests serve as an example but also make sure we don't change
+// the output of the random number generator when given a fixed seed.
+
+func Example() {
+	// Seeding with the same value results in the same random sequence each run.
+	// For different numbers, seed with a different value, such as
+	// time.Now().UnixNano(), which yields a constantly-changing number.
+	rand.Seed(42)
+	answers := []string{
+		"It is certain",
+		"It is decidedly so",
+		"Without a doubt",
+		"Yes definitely",
+		"You may rely on it",
+		"As I see it yes",
+		"Most likely",
+		"Outlook good",
+		"Yes",
+		"Signs point to yes",
+		"Reply hazy try again",
+		"Ask again later",
+		"Better not tell you now",
+		"Cannot predict now",
+		"Concentrate and ask again",
+		"Don't count on it",
+		"My reply is no",
+		"My sources say no",
+		"Outlook not so good",
+		"Very doubtful",
+	}
+	fmt.Println("Magic 8-Ball says:", answers[rand.Intn(len(answers))])
+	// Output: Magic 8-Ball says: As I see it yes
+}
+
+// This example shows the use of each of the methods on a *Rand.
+// The use of the global functions is the same, without the receiver.
+func Example_rand() {
+	// Create and seed the generator.
+	// Typically a non-fixed seed should be used, such as time.Now().UnixNano().
+	// Using a fixed seed will produce the same output on every run.
+	r := rand.New(rand.NewSource(99))
+
+	// The tabwriter here helps us generate aligned output.
+	w := tabwriter.NewWriter(os.Stdout, 1, 1, 1, ' ', 0)
+	defer w.Flush()
+	show := func(name string, v1, v2, v3 interface{}) {
+		fmt.Fprintf(w, "%s\t%v\t%v\t%v\n", name, v1, v2, v3)
+	}
+
+	// Float32 and Float64 values are in [0, 1).
+	show("Float32", r.Float32(), r.Float32(), r.Float32())
+	show("Float64", r.Float64(), r.Float64(), r.Float64())
+
+	// ExpFloat64 values have an average of 1 but decay exponentially.
+	show("ExpFloat64", r.ExpFloat64(), r.ExpFloat64(), r.ExpFloat64())
+
+	// NormFloat64 values have an average of 0 and a standard deviation of 1.
+	show("NormFloat64", r.NormFloat64(), r.NormFloat64(), r.NormFloat64())
+
+	// Int31, Int63, and Uint32 generate values of the given width.
+	// The Int method (not shown) is like either Int31 or Int63
+	// depending on the size of 'int'.
+	show("Int31", r.Int31(), r.Int31(), r.Int31())
+	show("Int63", r.Int63(), r.Int63(), r.Int63())
+	show("Uint32", r.Uint32(), r.Uint32(), r.Uint32())
+
+	// Intn, Int31n, and Int63n limit their output to be < n.
+	// They do so more carefully than using r.Int()%n.
+	show("Intn(10)", r.Intn(10), r.Intn(10), r.Intn(10))
+	show("Int31n(10)", r.Int31n(10), r.Int31n(10), r.Int31n(10))
+	show("Int63n(10)", r.Int63n(10), r.Int63n(10), r.Int63n(10))
+
+	// Perm generates a random permutation of the numbers [0, n).
+	show("Perm", r.Perm(5), r.Perm(5), r.Perm(5))
+	// Output:
+	// Float32     0.2635776           0.6358173           0.6718283
+	// Float64     0.628605430454327   0.4504798828572669  0.9562755949377957
+	// ExpFloat64  0.3362240648200941  1.4256072328483647  0.24354758816173044
+	// NormFloat64 0.17233959114940064 1.577014951434847   0.04259129641113857
+	// Int31       1501292890          1486668269          182840835
+	// Int63       3546343826724305832 5724354148158589552 5239846799706671610
+	// Uint32      2760229429          296659907           1922395059
+	// Intn(10)    1                   2                   5
+	// Int31n(10)  4                   7                   8
+	// Int63n(10)  7                   6                   3
+	// Perm        [1 4 2 3 0]         [4 2 1 3 0]         [1 2 4 0 3]
+}
+
+func ExamplePerm() {
+	for _, value := range rand.Perm(3) {
+		fmt.Println(value)
+	}
+
+	// Unordered output: 1
+	// 2
+	// 0
+}
+
+func ExampleShuffle() {
+	words := strings.Fields("ink runs from the corners of my mouth")
+	rand.Shuffle(len(words), func(i, j int) {
+		words[i], words[j] = words[j], words[i]
+	})
+	fmt.Println(words)
+
+	// Output:
+	// [mouth my the of runs corners from ink]
+}
+
+func ExampleShuffle_slicesInUnison() {
+	numbers := []byte("12345")
+	letters := []byte("ABCDE")
+	// Shuffle numbers, swapping corresponding entries in letters at the same time.
+	rand.Shuffle(len(numbers), func(i, j int) {
+		numbers[i], numbers[j] = numbers[j], numbers[i]
+		letters[i], letters[j] = letters[j], letters[i]
+	})
+	for i := range numbers {
+		fmt.Printf("%c: %c\n", letters[i], numbers[i])
+	}
+
+	// Output:
+	// C: 3
+	// D: 4
+	// A: 1
+	// E: 5
+	// B: 2
+}
+
+func ExampleIntn() {
+	// Seeding with the same value results in the same random sequence each run.
+	// For different numbers, seed with a different value, such as
+	// time.Now().UnixNano(), which yields a constantly-changing number.
+	rand.Seed(86)
+	fmt.Println(rand.Intn(100))
+	fmt.Println(rand.Intn(100))
+	fmt.Println(rand.Intn(100))
+
+	// Output:
+	// 42
+	// 76
+	// 30
+}