In the USA there is one doctor on every forty people.

[tufguy]

In the USA there is one doctor on every forty people.

Please check my sentence.

 

[Rover_KE]

In the USA there is one doctor for every forty people.

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[emsr2d2]

In the USA, there is one doctor [STRIKE]on[/STRIKE] for every forty people.

Please check my sentence.

See above.

I find that figure very unlikely. In 2014, the official (legal) population of the USA was almost 319 million. If your figure is correct, that means there were 7,975,000 doctors (almost 8 million). The only figure I can find online shows that there were 1,045,910 doctors (a little over 1 million). That's one doctor for every 305 people.