Line Up and Add

Can adding a whole number to a decimal really be as neat as stacking building blocks? Yes... if every digit stands above the SAME place. One tiny sideways slip can change the answer completely.

Picture a place-value grid with columns for tens, ones, tenths and hundredths. The decimal points form a bright vertical line. Each digit belongs in its own column. A six in the tenths column means six tenths, not simply the digit six. To add, write the numbers one above the other. Line up the decimal points first. If a whole number has no decimal point showing, imagine one after its ones digit. Add zero placeholders to the right when they help you see the columns. Those zeros do not change its value. Now add from the smallest place on the right, moving left one column at a time. If a column totals ten or more, write its ones digit and regroup one into the next column. Never slide digits together just because they are neighbours. PLACE value decides where each digit goes.

Let's work through an example. A school garden path is forty-seven metres long, and another section is three point six eight metres long. What is their total length? Write forty-seven above three point six eight, with the ones in one column and both decimal points aligned. Show forty-seven as forty-seven point zero zero. Start in the hundredths column. Zero plus eight equals eight, so eight appears in hundredths. In tenths, zero plus six equals six. The decimal point stays directly below the other decimal points. In the ones column, seven plus three equals ten. Write zero in the ones place, then regroup one ten into the tens column. In tens, four plus the regrouped one equals five. Read the result across: fifty point six eight metres. The total length is fifty point six eight metres.

Line up decimal points, add each place from right to left, and regroup when needed. Keep every digit in its proper column... and your decimal additions will stay accurate. You've got this!