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Lesson 4: Multiplying by tens

# More with multiplication and division: FAQ

## What do the letters in multiplication and division equations stand for?

The letters are variables - they can stand for any number.

## What is the associative property of multiplication?

The associative property of multiplication means that when we multiply three or more numbers together, we can group them in any way we want and still get the same answer. For example, $\left(2×3\right)×4$ is the same as $2×\left(3×4\right)$.

## What is special about multiplying by tens?

When you multiply a number by ten, you are essentially just adding a zero to the end of the number. This is because of how place value works.
For example, consider the number $34$. The "$3$" is in the tens place, and the "$4$" is in the ones place. When you multiply $34$ by $10$, you end up with $340$. The "$3$" has shifted over to the hundreds place, the "$4$" has shifted to the tens place, and the new zero is now in the ones place. This pattern holds true for any whole number: when you multiply by ten, you just add a zero to the end. This makes multiplying by ten relatively easy compared to multiplying by other numbers.

## How can I use the associative property to multiply $2$‍ -digit numbers?

The associative property of multiplication tells us that we can group factors in different ways and still get the same product. So when multiplying a $2$-digit number by a $1$-digit number, we can use the associative property to break down the $2$-digit number into two separate $1$-digit multiplications, and then combine the two products to get the final answer.
$28$ is the same as $7$ groups of $4$.
$\begin{array}{rl}28×2& =7×4×2\\ \\ & =7×\left(4×2\right)\\ \\ & =7×8\\ \\ & =56\end{array}$

## Want to join the conversation?

• why have a whole passage about math if you can just watch videos?
• Different people like to learn in different ways. For some watching videos makes more sense to them, for others reading, and for others even more unique methods! It can also be very helpful to use multiple learning strategies in combination in order to gain a more solid understanding of a topic! Try it out!
• what if we forget
• you can always read it again and do exercise after a while to remember it. It's called spaced repetition
• This is really really important!
• Hey
what is 100x100
• 10000.
Just add x100 to 100 (means add 00 to the back of 100).
Hope this helps!!^-^
(1 vote)
• I think that this unit has been the hardest for me so far .But now I understand most of it! It has been
exciting leaning all these new things!
(1 vote)
• why
is it the same?
(1 vote)