How is the 2.4 = 12 and also multiplied by 5

2.4057 is very close to 2.4.

2.4 can be written as a fraction:

$$2.4 = \frac{24}{10}$$

This fraction can be simplified by dividing both the numerator and the denominator by their greatest common divisor, which is 2:

$$\frac{24}{10} = \frac{24 \div 2}{10 \div 2} = \frac{12}{5}$$

Since the ratio of H is approximately $\frac{12}{5}$, multiplying both the C and H ratios by the denominator (5) will convert both to whole numbers:
For C: $1 \times 5 = 5$
For H: $\frac{12}{5} \times 5 = 12$

This gives the whole number ratio of C:H as $5:12$, leading to the empirical formula $C_5 H_{12}$.