| MECHANICAL DEVICES SOLUTION | 
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| | DEVICE 1 has three hollows and three protrusions |  | DEVICE 2 has four hollows and three protrusions |  | DEVICE 3 has three hollows and four protrusions |  | DEVICE 4 only has four hollows and cannot be moved | 
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| Device 3 is the only one with four protrusions, so it must fit into device 4 (four hollows) | 
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| Devices 1 and 2 both have three protrusions, so either will fit into the hollows on the back of device 3, but: (a) The back of device 2 has four hollows, so device 1 (three protrusions) won't fit;
 (b) The back of device 1 has three hollows, so device 2 (three protrusions) will fit
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| Therefore device 1 must be inserted into the back of device 3 and device 2 is fitted last | 
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| HOW TO MANIPULATE THE DEVICES | 
| | 01) Rotate the energy beam to flow from 3 to 1, then move 3 to the centre |  | 02) Rotate the energy beam to flow from 2 to 4, then move 3 into 4 Note that the protrusions on 3 must be facing towards 4
 |  | 03) Rotate the energy beam to flow from 1 to 3, then move 1 to the centre |  | 04) Rotate the energy beam to flow from 2 to 4, then move 1 into the back of 3 Note that the protrusions on 1 must be facing towards 4 (the back of 3)
 |  | 05) Rotate the energy beam to flow from 2 to 4, then move 2 to the centre Note that initially the protrusions will be facing the wrong way
 |  | 06) While 2 is in the centre rotate the energy beams to flow from 4 to 2 |  | 07) Return 2 to it's original position Note that now the protrusions are facing the correct way
 |  | 08) Rotate the energy beam to flow from 2 to 4, then move 2 into the back of 1 | 
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