<_title>Practice the addition operation <_description>Answer some algebra questions <_prerequisite>Simple addition. Can recognize written numbers <_goal>In a limited time, find the sum of of two numbers. Introduction to simple in-line addition. <_manual>An addition problem with two numbers is displayed. At the right of the equals sign, give the answer, the sum. Use the left and right arrows to modify your answer and press the Enter key to check if you've got it right. If not, just try again.