Lesson 1: Divide two- and three-digit dividends by multiples of 10 with single-digit quotients, and make connections to a written method.

Property

To estimate the quotient when dividing by a multiple of 10, use basic division facts. Think of the dividend and divisor in terms of tens.
For example, to solve $84 \div 20$, you can think of it as $8 \text{ tens} \div 2 \text{ tens}$, which simplifies to $8 \div 2$.

Examples

• To estimate $72 \div 30$, think: How many 3s are in 7? The answer is 2. So, $72 \div 30 \approx 2$. ($60 \div 30 = 2$)
• To estimate $154 \div 50$, think: How many 5s are in 15? The answer is 3. So, $154 \div 50 \approx 3$. ($150 \div 50 = 3$)
• To estimate $430 \div 60$, think: How many 6s are in 43? The answer is 7. So, $430 \div 60 \approx 7$. ($420 \div 60 = 7$)

Explanation

Estimating helps you find an answer that is close to the exact quotient before you start long division. By using basic facts, you can simplify the problem and make a reasonable guess. This strategy is useful for determining the first digit of your quotient in the standard algorithm. It also helps you check if your final answer makes sense.

Property

To divide a dividend by a divisor using the standard algorithm, we find a quotient ($q$) and a remainder ($r$) such that

Examples