Line up the points · Alberta Grade 4 · maddyhelps.com
Money is the easiest way in: dollars and cents are decimals already. Every number is written with two places after the point — 4.6 is written 4.60 — so the points line up and each column means one thing.
Why is 4.6 the same as 4.60?
Which is bigger? Each square is one hundredth.
0.5
0.45
Decimals in columns
$16.23, $17.25, $7.35, $6.75, $21.49, $5.25. 4.6 is 4 and 6 tenths; 4.60 is 4 and 60 hundredths, and 60 hundredths is 6 tenths. Writing the zero changes nothing except that the columns now line up. 0.5 is bigger: 50 hundredths against 45. Reading 0.45 as bigger because 45 is more than 5 is the most common decimal mistake there is, and the grids show why it is wrong.
The mistake to watch for is lining numbers up on the right, as with whole numbers. With decimals the point decides the columns, and $4.6 + $2.75 done right-aligned gives nonsense.
Why this matters is on the numbers to 10 000 page. More sheets