I.

1. The Pins 2 and 3 are connected to ground. This is made so that they can act as a reset.
2. The Pins 2 and 3 will reset to 0000
3. Pins 6 and 7 are also connected to ground and in the same function, they also act as a reset.
4. But unlike that of Pins 2 and 3, when 6 and 7 are raised to logic 1, they are will reset to a 1001 configuration.
5. Connecting pin 1 to pin 12 is made so that the output for pin 12 would be the output for pin 1. This is made since the 7490 is divided into 2, pins 1 and 12 makes the necessary connection between the 2 parts. If it was not for the connection, the LED’s would not light alternately in order (maybe in random).
6. The output pins of the 7490 are the pins 12, 9, 8 and 11

II.

1. The input pins of the 7442 are pins 15,14,13 and 12.
2. The input pins are connected to the "output" pins from the 7490 which is pin 12,9,8 and 11.
3. The LED’s that were connected to the 7442 lighted up alternately in order, in simpler terms the 7442 made the LED "dance". This is made possible because the 7442 allows the current to pass at only one out of it’s 8 output pins depending on what combination of currents ( 1’s and 0’s) it receives from it’s input, hence the name of "decoder".

III.

1. The input pins of the 7447 are pins 7,1,2 and 6
2. The input pins of the 7447 are connected to the input pins of the 7490 which was 12,4,8 and 11 respectively.
3. The LED’s also light up alternately in order. It has the same function as the 7442 in which the chip allows the current to pass at only one of it’s 8 output pins depending on the combination of currents (1’s and 0’s) it receives in it’s input. The only difference I think with this and the 7442 is the 7447 might be designed for LED’s that form numbers. So that for example the combination 0001 ( 1 in binary terms) will display the actual number "1" in the LEDs’ display.

IV.

The experiment was all about how to make lights dance in order. This is made possible by 3 chips. The 555, the 7490 and the 7442/7447. What the 555 chip does is that it can only signal 2 numbers, 1 and 0 . The 555 is connected to the 7490 chip which purpose is to translate the 1’s and 0’s of the 555 into numbers. The 7490 will then "send" the number to the 7447/7442 chip. When the chips receive the number that the 7490 sent, it will light up the light that corresponds do that number.