Decimals are an essential part of mathematics, and understanding how to work with them is vital for success in many areas of life. One of the fundamental operations involving decimals is multiplication. In this blog post, we will focus on multiplying decimals by a whole number, up to two digits. We will explore a step-by-step approach to help students master this skill, including visual representation and practical exercises.
Let’s consider the following example: almonds are sold in packets of 0.25 kg, and we want to know how much 15 packets weigh. Initially, students might attempt to add 0.25 fifteen times to find the answer, but this approach is tedious and time-consuming. Therefore, we need to teach students a more efficient method for solving this problem, which involves decimal multiplication.
To help students understand decimal multiplication, it’s useful to start with a visual representation. We can use decimal discs, which are small circles that represent decimal values.Once students have created their decimal discs, we can move on to the multiplication process.
To multiply a decimal by a whole number, we follow these steps:
Write the numbers in column form, with the decimal points aligned.
Ignore the decimal point for the time being and multiply the number by the ones digit of the whole number.
Write down the result below the first row.
Multiply the same number by the tens digit of the whole number and write down the result below the first row, shifted one place to the left.
Add up the two rows to get the final answer.
Place the decimal point in the answer, starting from the right, after the same number of decimal places as in the original question.
Let’s go back to our almonds example and apply this approach:
0.25 × 15 = ?
Therefore, 15 packets of almonds weigh 3.75 kg.
After understanding the step-by-step approach, students can practice multiplying decimals by whole numbers using different methods. For example, we can pair students and give each one a dice. One student writes a decimal number up to two decimal places, and the other rolls the dice twice and multiplies the number on the mini-board with whatever comes on the dice. The students can use mental math, decimal/number discs, or mini boards/papers to construct models.
Multiplying decimals by a whole number up to two digits is an essential skill for mathematics and daily life. We can teach students a step-by-step approach using visual representation and practical exercises. By following this approach, students can solve multiplication problems efficiently and accurately.
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