Max Rescues the Mermaid Pearl: Adding Tens Challenge

About this Grade 2 Adding Multiples Of 10 Drill

Adding multiples of 10 is a foundational skill that bridges early counting strategies into flexible mental math—exactly where second graders need to be developmentally. When children master 23 + 10 or 45 + 20, they're learning that the ones place stays the same while only the tens place changes. This insight helps them see numbers as groups of tens and ones, which strengthens their place-value understanding across all addition and subtraction. By age 7 or 8, students are ready to move beyond counting by ones and start recognizing patterns, and adding multiples of 10 makes this pattern-spotting concrete and rewarding. This skill directly supports their ability to add two-digit numbers more efficiently and builds confidence with mental math strategies they'll use throughout elementary school. Real-world applications appear constantly—calculating money, estimating items in groups, or even thinking like a mermaid counting collections of shells in groups of ten.

What your student will practice

• Recognize that adding multiples of 10 changes only the tens digit
• Fluently add one or two multiples of 10 to a two-digit number
• Apply place-value understanding to solve addition problems mentally
• Explain their thinking using tens and ones language

Common mistakes to watch for

Many second graders add multiples of 10 by treating all digits equally—for example, answering 34 + 20 as 54 instead of 54, or worse, writing 314 by adding digits left to right without understanding place value. Another common error is counting up by ones instead of jumping by tens (saying 34, 35, 36... instead of 34, 44, 54), which defeats the purpose of the strategy. Parents and teachers can spot this by asking the child to show their work with drawings of tens-and-ones blocks or by listening to how they verbalize the problem—if they count by ones, that's the red flag to refocus on the pattern.