1. The problem is to understand how to divide a whole number by a decimal number and find the quotient. 2. The key formula or rule is: When dividing by a decimal, multiply both the dividend (the number being divided) and the divisor (the decimal number) by the same power of 10 to make the divisor a whole number. 3. For example, if you want to divide $12 \div 0.4$, multiply both by 10 to get $\frac{12 \times 10}{0.4 \times 10} = \frac{120}{4}$. 4. Now divide $120 \div 4 = 30$. 5. This method works because multiplying numerator and denominator by the same number is equivalent to multiplying by 1, which does not change the value. 6. Always remember to shift the decimal point in both numbers the same number of places to the right to convert the divisor into a whole number before dividing. 7. This makes division easier and avoids dealing with decimals in the divisor. Final answer: $12 \div 0.4 = 30$.