Multiplying by Multiples of Ten

Have you ever needed to multiply a number by $10$, $20$, $30$, or even $50$? These numbers are called multiples of ten because they end in a zero. Multiplying with them is much easier than it looks, thanks to a simple shortcut called the "Zero Trick"!

The "Zero Trick" Strategy

When you multiply a single-digit number by a multiple of ten, you don't need to count by big numbers. Just follow these two easy steps:

Example: $4 \times 30$

1. Ignore the zero(s) for a moment and multiply the non-zero digits. In $4 \times 30$, the non-zero digits are $4$ and $3$. $4 \times 3 = 12$
2. Count the number of zeros you ignored, and add them to the end of your answer. We ignored one zero in $30$. So, we place one zero at the end of $12$. $4 \times 30 = 120$

Multiplying Two Multiples of Ten

You can use the exact same trick if both numbers are multiples of ten!

Example: $20 \times 50$

1. Multiply the non-zero digits. The non-zero digits are $2$ and $5$. $2 \times 5 = 10$
2. Count the zeros and add them back. There is one zero in $20$ and one zero in $50$. That makes two zeros we need to add to our answer. Add two zeros to the end of $10$: $20 \times 50 = 1000$

Let's Practice

Let's try one more example together: $7 \times 60$

• First, multiply the non-zero digits: $7 \times 6 = 42$
• Next, count the zeros: There is one zero in $60$.
• Finally, attach that zero to your answer: $7 \times 60 = 420$

Remember, whether you have one zero or two zeros, just multiply the front numbers and tag the total number of zeros onto the end!