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docs/reference/js/lessons/strobe-light/challenges.md

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+# strobe light challenges
+
+Coding challenges for the strobe light tutorial. #docs
+
+## Before we get started
+
+Complete the following guided tutorial:
+
+* [tutorial](/microbit/lessons/strobe-light/tutorial)
+
+At the end of the tutorial, click `keep editing`. Your code should look like this:
+
+```
+for (let i = 0; i < 5; i++) {
+    for (let j = 0; j < 5; j++) {
+        led.plot(i, j)
+        basic.pause(200)
+    }
+}
+```
+
+### Challenge 1
+
+### @video td/videos/strobe-light-1
+
+Make the LEDs light up faster by changing the **pause** from 200 to 100 milliseconds:
+
+```
+for (let i1 = 0; i1 < 5; i1++) {
+    for (let j1 = 0; j1 < 5; j1++) {
+        led.plot(i1, j1)
+        basic.pause(100) // ***
+    }
+}
+```
+
+* Run the code to see if it works as expected.
+
+### Challenge 2
+
+### @video td/videos/strobe-light-2
+
+Make the board light up by rows instead of by columns by swapping the `i` and `j` variables in `led->plot(i, j)`.
+
+```
+for (let i2 = 0; i2 < 5; i2++) {
+    for (let j2 = 0; j2 < 5; j2++) {
+        led.plot(j2, i2) // ***
+        basic.pause(100)
+    }
+}
+```
+
+* Run the code to see if it works as expected.
+
+### Challenge 3
+
+### @video td/videos/strobe-light-ultimate
+
+Now that all the LEDs are lit up, let's make them turn off by reversing the strobe light pattern! You can use `led->unplot` to turn off a single LED.
+
+```
+for (let i3 = 0; i3 < 5; i3++) {
+    for (let j3 = 0; j3 < 5; j3++) {
+        led.plot(j3, i3)
+        basic.pause(100)
+    }
+}
+for (let k = 0; k < 5; k++) {
+    for (let l = 0; l < 5; l++) {
+        led.unplot(4 - l, 4 - k) // ***
+        basic.pause(100) // ***
+    }
+}
+```
+