How many lakhs make five billion?

We know that,

1 crore = 100 lakh

1 billion = 100 crore = 100 $\times$ 100 lakh

$\Rightarrow$ 1 billion = 10,000 lakh

$\Rightarrow$ 5 billion = 5 $\times$ 10,000 lakh = 50,000 lakh