Calculating GPH

[eternitybc]

I hopefully have a simple question. If I have a 1 foot run of 1” pipe followed by 1 foot run of ¾” pipe followed by another 1 foot run of 1” pipe do I calculate the GPH by using the smallest diameter pipe, or do I calculate it for each and add them together?
Example:
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What gets me confused is in this case wouldn’t the friction loss be less than if the whole pipe is ¾”?