Unit 3: Subtraction (10/11) -- Adult Literacy Fundamental Mathematics: ...

Unit 3: Subtraction Topic E: Estimating Answers in Subtraction You have learned how to round numbers. Now you can use that skill in rounding numbers to find an approximate difference. By estimating your answer first, you can tell if your answer is sensible. In these examples, estimate the answer. Round each number BEFORE you subtract. Example A: [latex]\begin{array}[t]{rrrrr} &47&\text{rounds to}&&50 \\-&26&\text{rounds to}&-&30 \\ \hline &&&&20 \end{array}[/latex] Example B: [latex]\begin{array}[t]{rrrrr} &870&\text{rounds to}&&900 \\-&342&\text{rounds to}&-&300 \\ \hline &&&&600 \end{array}[/latex] Example C: [latex]\begin{array}[t]{rrrrr} &24\,397&\text{rounds to}&&20\,000 \\-&6\,148&\text{rounds to}&-&6\,000 \\ \hline &&&&14\,000 \end{array}[/latex] Usually you estimate to the largest place value that you can. Exercise One Estimate the differences. Round the numbers before you subtract. Check your work using the answer key at the end of the exercise. - [latex]\begin{array}[t]{rrrrr}&9\,963&\approx&&10\,000 \\-&7\,099&\approx&-&7\,000 \\ \hline &&&&3\,000 \end{array}[/latex] - [latex]\begin{array}[t]{rrrrr}&70\,534&\approx&&70\,000 \\-&7\,689&\approx&-&8\,000 \\ \hline &&&&62\,000 \end{array}[/latex] - [latex]\begin{array}[t]{rr}&687\\-&438\\ \hline \\ \end{array}[/latex] - [latex]\begin{array}[t]{rr}&754\\-&236\\ \hline \\ \end{array}[/latex] - [latex]\begin{array}[t]{rr}&8\,442\\-& 1\, 876\\ \hline \\ \end{array}[/latex] - [latex]\begin{array}[t]{rr}&5 \,630\\-& 1 \,752\\ \hline \\ \end{array}[/latex] - [latex]\begin{array}[t]{rr}&5 \,342\\-& 3 \,647\\ \hline \\ \end{array}[/latex] - [latex]\begin{array}[t]{rr}&7 \,111\\-& 5 \,982\\ \hline \\ \end{array}[/latex] - [latex]\begin{array}[t]{rr}&6 \,031 \\-& 2\, 899\\ \hline \\ \end{array}[/latex] - [latex]\begin{array}[t]{rr}&41 \,573\\-& 4\, 846\\ \hline \\ \end{array}[/latex] - [latex]\begin{array}[t]{rr}&36 \,154\\-& 9 \,038\\ \hline \\ \end{array}[/latex] - [latex]\begin{array}[t]{rr}&46 \,124 \\-& 9 \,762\\ \hline \\ \end{array}[/latex] - [latex]\begin{array}[t]{rr}&54 \,751 \\-& 7 \,896\\ \hline \\ \end{array}[/latex] - [latex]\begin{array}[t]{rr}&72 \,450 \\-& 31\, 924\\ \hline \\ \end{array}[/latex] - [latex]\begin{array}[t]{rr}&81 \,692 \\-& 53\, 908\\ \hline \\ \end{array}[/latex] - [latex]\begin{array}[t]{rr}&92 \,163 \\-& 45\, 517\\ \hline \\ \end{array}[/latex] - [latex]\begin{array}[t]{rr}&171 \,234\\-& 82\, 169\\ \hline \\ \end{array}[/latex] - [latex]\begin{array}[t]{rr}&102 \,085 \\-& 36 \,526\\ \hline \\ \end{array}[/latex] Answers to Exercise One - 10000 − 7000 = 3000 - 70000 − 8000 = 62000 - 700 − 400 = 300 - 800 − 200 = 600 - 8000 − 2000 = 6000 - 6000 − 2000 = 4000 - 5000 − 4000 = 1000 - 7000 − 6000 = 1000 - 6000 − 3000 = 3000 - 40000 − 5000 = 35000 - 40000 − 9000 = 31000 - 50000 − 10000 = 40000 - 50000 − 8000 = 42000 - 70000 − 30000 = 40000 - 80000 − 50000 = 30000 - 90000 − 50000 = 40000 - 170000 − 80000 = 90000 - 100000 − 40000 = 60000 Estimating Answers in Subtraction Wo