Grade 1 · Number and Operations in Base Ten

CCSS.MATH.CONTENT.1.NBT.C.5

Given a two-digit number, mentally find 10 more or 10 less than the number, without having to count; explain the reasoning used.

Read this standard on the official Common Core site

Lessons that teach this standard

• Adding Tens and Ones Within 100

  First grade: find 10 more or 10 less in your head, add and subtract tens, and add within 100 by adding tens to tens and ones to ones, making a new ten when needed.