Hi Anish,

Percent means "per one-hundred" so 2.5 percent is $\large\frac{2.5}{100}$ and 1 billion is 1,000,000,000 so 1.5 billion is $1.5 \times 1,000,000,000.$Hence 2.5 percent of 1.5 billion is

\[\frac{2.5}{100} \times 1.5 \times 1,000,000,000.\]

Rewriting this I get

\[2.5 \times 1.5 \times 10,000,000 = 3.75 \times 10,000,000= 37.5 \times 1,000,000.\]

Since 1 million is 1,000,000 we have 2.5 percent of 1.5 billion is 37.5 million.

Penny