Grade 5Math

Standard Algorithm with Decimal Divisors

Grade 5 students learn the standard algorithm for dividing decimals by decimal divisors in Eureka Math, Chapter 25. The key strategy is to multiply both the dividend and divisor by the same power of 10 to convert the divisor into a whole number, making long division straightforward. This skill builds fluency with decimal operations and place value reasoning.

Key Concepts

Property To divide by a decimal, first convert the divisor into a whole number by multiplying both the divisor and the dividend by the same power of 10. This is equivalent to moving the decimal point in both numbers the same number of places to the right. Then, perform division as usual. $a \div b = (a \times 10^n) \div (b \times 10^n)$.

Examples To solve $9.6 \div 0.8$, we can rewrite it as $96 \div 8$. The quotient is $12$. To solve $15.75 \div 0.25$, we multiply both numbers by $100$ to get $1575 \div 25$. The quotient is $63$. To solve $4.83 \div 0.7$, we multiply both numbers by $10$ to get $48.3 \div 7$. The quotient is $6.9$.

Explanation This skill applies the standard division algorithm directly to problems with decimal divisors. The first step is to make the divisor a whole number by moving its decimal point to the right. You must then move the decimal point in the dividend the same number of places to the right to keep the problem equivalent. After adjusting the decimal points, place the decimal for the quotient directly above its new position in the dividend and divide as you would with whole numbers.

Common Questions

How do you divide by a decimal number?

To divide by a decimal, multiply both the dividend and divisor by the same power of 10 to make the divisor a whole number. For example, 9.6 ÷ 0.8 becomes 96 ÷ 8 = 12.

What is the standard algorithm for decimal divisors?

The standard algorithm for decimal divisors involves shifting the decimal point in both numbers the same number of places to the right until the divisor is a whole number, then performing regular long division.

Why do we multiply both numbers by the same power of 10 when dividing decimals?

Multiplying both the dividend and divisor by the same value keeps the quotient the same, because dividing the numerator and denominator of a fraction by the same number does not change its value.

What grade level is this decimal division skill?

This skill is taught in Grade 5 as part of Eureka Math, Chapter 25: Division of Fractions and Decimal Fractions.

What are some examples of dividing with decimal divisors?

Examples include 9.6 ÷ 0.8 = 12 (rewrite as 96 ÷ 8), 15.75 ÷ 0.25 = 63 (rewrite as 1575 ÷ 25), and 4.83 ÷ 0.7 = 6.9 (rewrite as 48.3 ÷ 7).