Common Core State Standard
2.OA.B.2
Fluently add and subtract within 20 using mental strategies. By end of Grade 2, know from memory all sums of two one-digit numbers.

CCSS: 2.OA.B.2, 3.OA.C.7
Choose to control the traffic by addition, subtraction or division. Avoid accidents while keeping the traffic flowing. Watch out for the pedestrians and be sure to let the emergency vehicles through.