How is total raw calculated for Science Pack 2?

I don’t understand how the total resource needed is calculated to produce one Science pack 2 (green one).

According to the Factorio wiki,
Science pack 2 requires:

• 1 Inserter
• 1 Transport belt

Calculation for one Inserter

According to the Factorio wiki
an Inserter requires:

• 1 Green circuit
• 1 Iron gear
• 1 Iron plate

According to the Factorio wiki
a Green circuit requires:

• 3 Copper cables
• 1 Iron plate

According to the Factorio wiki
an Iron gear requires:

• 2 Iron plates

According to the Factorio wiki
Copper cable requires (to produce 2):

• 1 Copper plate (1.5 Copper plate to produce 3 units)

So, to produce 1 Inserter, we need 4 Iron plates + 1.5 Copper plates.

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Calculation for Transport belt

According to the Factorio wiki
a Transport belt requires:

• 1 Iron gear ( requires 2 Iron plates )
• 1 Iron plate

So, to produce 1 Transport belt, we need 3 Iron plates.

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Then, to produce one Science Pack 2, we need 7 Iron plates and 1.5 Copper plates.

Why is the total raw 5.5 Iron plates and 1.5 Copper plates?