Theme 9.  Problems to find the unknown subtrahend

In the theme you learn:
• You will practice adding and subtracting two-digit numbers up to 100 by place value;
• You will remember how to find the unknown subtrahend;
• You will learn to solve problems to find the unknown subtrahend;
• You will practice adding and subtracting round numbers in a "chain";
• You will choose solutions to problems and find the mistake in the solution;
• You will practice comparing an expression and a number.