Find (1) If \( 31 \times 25=775 \), then \( 0.31 \times 2.5=\ldots \ldots \) (2) Fifth of \( 15=\ldots \ldots \ldots . \).

To start, since \( 31 \times 25 = 775 \), you can shift the decimal points to find \( 0.31 \times 2.5 \). Notice that if you multiply \( 0.31 \) by \( 2.5 \), you are effectively scaling down \( 31 \times 25 \) by a factor of \( 10 \) for each decimal point movement. So, \( 0.31 \times 2.5 = \frac{775}{100} = 7.75 \). Next up, what is a fifth of \( 15 \)? To find this, simply divide \( 15 \) by \( 5 \). So, \( \frac{15}{5} = 3 \). Therefore, a fifth of \( 15 \) is \( 3 \).