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Mental Math Worksheets

13 free PDFsUS Letter or A4Answer key includedNo login

Mental math for 2nd grade: 10 more, 10 less, 100 more and 100 less, adding and subtracting tens and hundreds, and the make a ten, make a hundred and count up strategies.

Download the mental math worksheets

10 more, 10 less, 100 more, 100 less

Fill in the 10 and 100 more and less table, add and subtract 10 and 100, and add and subtract whole tens and hundreds.

Mental math strategies

Make a ten, make a hundred, count up to subtract, and add and subtract tens within 100.

Print at 100% (actual size) for the cleanest tracing lines.

About these mental math worksheets

Mental math means working a problem out in your head with a smart strategy instead of a pencil and columns. In 2nd grade the key skills are adding and subtracting 10 and 100 to numbers up to 900, and using place value to add and subtract within 100.

These worksheets practice 10 more, 10 less, 100 more and 100 less in a table and in number sentences, then adding and subtracting whole tens and hundreds. Strategy pages break each problem into small steps: make the next ten (48 + 7 = 48 + 2 + 5), make a hundred, and count up to subtract (53 − 48: 2 to 50, 3 more to 53).

Most pages come as Sheet A and B. Every page has an answer key on page 2, and all pages print in black and white on US Letter or A4.

Standards

  • CCSS.MATH.CONTENT.2.NBT.B.8Mentally add 10 or 100 to a given number 100–900, and mentally subtract 10 or 100 from a given number 100–900.
  • CCSS.MATH.CONTENT.2.NBT.B.5Fluently add and subtract within 100 using strategies based on place value, properties of operations, and/or the relationship between addition and subtraction.
  • CCSS.MATH.CONTENT.2.NBT.B.7Add and subtract within 1000, using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method. Understand that in adding or subtracting three-digit numbers, one adds or subtracts hundreds and hundreds, tens and tens, ones and ones; and sometimes it is necessary to compose or decompose tens or hundreds.

How to use them

  1. Start with 10 More, 10 Less, 100 More, 100 Less. Ask which digit changes and why.
  2. Use Add and Subtract 10 and 100 as a quick warm-up, a few minutes a day.
  3. Teach one strategy at a time: make a ten, then count up to subtract, then make a hundred.
  4. Ask children to say their thinking out loud. The steps on the page are the words to use.

Teaching tips

  • Adding 10 changes the tens digit; adding 100 changes the hundreds digit. 395 + 10 = 405 crosses a hundred, so two digits change.
  • Make a ten: 38 + 6 is 38 + 2 = 40, then 40 + 4 = 44.
  • Count up to subtract when the numbers are close: 72 − 68 is 2 to 70 and 2 more, so 4.
  • Use a hundred chart or an open number line until the steps are easy in your head.

Questions teachers and parents ask

What mental math should a 2nd grader know?

Second graders add and subtract within 20 from memory, add and subtract 10 and 100 to numbers from 100 to 900 in their heads, and use place value to add and subtract within 100.

What is the make a ten strategy?

To add 48 + 7, first add 2 to make 50, then add the 5 that is left: 48 + 7 = 55. Getting to a ten (or a hundred) first makes the rest easy.

Are there answer keys?

Yes. Every page has an answer key on page 2 with every step filled in.