indefinite article

[Lenka]

"During the 20th century, an estimated 70 million people died from famines across the world, of whom an estimated 30 million died during the famine of 1958–61 in China. "(source: Famine - Wikipedia, the free encyclopedia)

Why is "an", the indefinite article, used in the sentence? It refers to a lural noun, doesn't it?

[Jason72]

It refers to 70 milion/30 milion which is in singular.

[aous02]

We can substitue 70/30 millions with "this number". So it's singular.
In the same way we say
*10 miles is (not are) a long way. Because we can replace 10 moles by this distance.
I hope this makes sense for you.

[Jason72]

Because we can replace 10 moles by this distance.

Moles?

[Lenka]

Thank you very much :)