Add solved exercises

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diff --git a/go/space-age/README.md b/go/space-age/README.md
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+# Space Age
+
+Given an age in seconds, calculate how old someone would be on:
+
+   - Mercury: orbital period 0.2408467 Earth years
+   - Venus: orbital period 0.61519726 Earth years
+   - Earth: orbital period 1.0 Earth years, 365.25 Earth days, or 31557600 seconds
+   - Mars: orbital period 1.8808158 Earth years
+   - Jupiter: orbital period 11.862615 Earth years
+   - Saturn: orbital period 29.447498 Earth years
+   - Uranus: orbital period 84.016846 Earth years
+   - Neptune: orbital period 164.79132 Earth years
+
+So if you were told someone were 1,000,000,000 seconds old, you should
+be able to say that they're 31.69 Earth-years old.
+
+If you're wondering why Pluto didn't make the cut, go watch [this
+youtube video](http://www.youtube.com/watch?v=Z_2gbGXzFbs).
+
+## Simple Stub
+
+The space_age.go "stub file" contains only one line with the correct
+package name and nothing more.  This will be the usual pattern for future
+exercises.  You will need to figure out the function signature(s).
+
+One way to figure out the function signature(s) is to look
+at the corresponding \*\_test.go file. It will show the package level
+functions(s) that the test will use to verify the solution.
+
+## Planet Type
+
+The test cases make use of a custom `Planet` type that is sent to your function.
+You will need to implement this custom type yourself.
+Implementing this new custom type as a string should suffice.
+
+
+## Coding the solution
+
+Look for a stub file having the name space_age.go
+and place your solution code in that file.
+
+## Running the tests
+
+To run the tests run the command `go test` from within the exercise directory.
+
+If the test suite contains benchmarks, you can run these with the `--bench` and `--benchmem`
+flags:
+
+    go test -v --bench . --benchmem
+
+Keep in mind that each reviewer will run benchmarks on a different machine, with
+different specs, so the results from these benchmark tests may vary.
+
+## Further information
+
+For more detailed information about the Go track, including how to get help if
+you're having trouble, please visit the exercism.io [Go language page](http://exercism.io/languages/go/resources).
+
+## Source
+
+Partially inspired by Chapter 1 in Chris Pine's online Learn to Program tutorial. [http://pine.fm/LearnToProgram/?Chapter=01](http://pine.fm/LearnToProgram/?Chapter=01)
+
+## Submitting Incomplete Solutions
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.
diff --git a/go/space-age/cases_test.go b/go/space-age/cases_test.go
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+package space
+
+// Source: exercism/problem-specifications
+// Commit: 28b3dac0 space-age: restrict seconds to fit within 32-bit int range
+// Problem Specifications Version: 1.2.0
+
+var testCases = []struct {
+	description string
+	planet      Planet
+	seconds     float64
+	expected    float64
+}{
+	{
+		description: "age on Earth",
+		planet:      "Earth",
+		seconds:     1000000000,
+		expected:    31.69,
+	},
+	{
+		description: "age on Mercury",
+		planet:      "Mercury",
+		seconds:     2134835688,
+		expected:    280.88,
+	},
+	{
+		description: "age on Venus",
+		planet:      "Venus",
+		seconds:     189839836,
+		expected:    9.78,
+	},
+	{
+		description: "age on Mars",
+		planet:      "Mars",
+		seconds:     2129871239,
+		expected:    35.88,
+	},
+	{
+		description: "age on Jupiter",
+		planet:      "Jupiter",
+		seconds:     901876382,
+		expected:    2.41,
+	},
+	{
+		description: "age on Saturn",
+		planet:      "Saturn",
+		seconds:     2000000000,
+		expected:    2.15,
+	},
+	{
+		description: "age on Uranus",
+		planet:      "Uranus",
+		seconds:     1210123456,
+		expected:    0.46,
+	},
+	{
+		description: "age on Neptune",
+		planet:      "Neptune",
+		seconds:     1821023456,
+		expected:    0.35,
+	},
+}
diff --git a/go/space-age/go.mod b/go/space-age/go.mod
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+module space
+
+go 1.13
diff --git a/go/space-age/space_age.go b/go/space-age/space_age.go
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+++ b/go/space-age/space_age.go
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+package space
+
+type Planet string
+
+func Age(seconds float64, planet Planet) float64 {
+	const earthSeconds float64 = 31557600
+
+	switch planet {
+	case "Mercury":
+		return seconds / (0.2408467 * earthSeconds)
+	case "Venus":
+		return seconds / (0.61519726 * earthSeconds)
+	case "Earth":
+		return seconds / (1.0 * earthSeconds)
+	case "Mars":
+		return seconds / (1.8808158 * earthSeconds)
+	case "Jupiter":
+		return seconds / (11.862615 * earthSeconds)
+	case "Saturn":
+		return seconds / (29.447498 * earthSeconds)
+	case "Uranus":
+		return seconds / (84.016846 * earthSeconds)
+	case "Neptune":
+		return seconds / (164.79132 * earthSeconds)
+	}
+	return -1
+}
diff --git a/go/space-age/space_age_test.go b/go/space-age/space_age_test.go
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+package space
+
+import (
+	"math"
+	"testing"
+)
+
+func TestAge(t *testing.T) {
+	const precision = 0.01
+	for _, tc := range testCases {
+		actual := Age(tc.seconds, tc.planet)
+		if math.IsNaN(actual) || math.Abs(actual-tc.expected) > precision {
+			t.Fatalf("FAIL: %s\nExpected: %#v\nActual: %#v", tc.description, tc.expected, actual)
+		}
+		t.Logf("PASS: %s", tc.description)
+	}
+}
+
+func BenchmarkAge(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		for _, tc := range testCases {
+			Age(tc.seconds, tc.planet)
+		}
+	}
+}