87−49=87−(50−1)=87−50+1=37+1=3887 minus 49 equals 87 minus open paren 50 minus 1 close paren equals 87 minus 50 plus 1 equals 37 plus 1 equals 38 4. Direct Subtraction by Parts : Technique : Subtract the tens first, then the units ( Step-by-step :
: Swap the terms and express the second as a difference ( Step-by-step :
Here is the complete solution for problem from the 7th-grade Algebra textbook by Dorofeev, Suvorova, and Bunimovich.
This exercise asks to write a chain of numerical equalities using specific mental calculation techniques. 1. Addition of a Two-Digit Number : Technique : Break the second number into tens and units ( Step-by-step :