Twelve decimal addition problems plus three word problems and a missing-number challenge, for Grade 5.
Try these before or after you print the worksheet. Most pairs below have a different number of decimal places on purpose, because that is where nearly every mistake comes from. The wrong answers offered are the ones you really get by lining the digits up instead of the decimal points.
8.4 + 3.27 = ?
11.67. Write 8.4 as 8.40 so both numbers have the same number of decimal places, then add column by column. Lining the digits up on the right instead gives 4.11, which is the usual slip.
0.9 + 0.56 = ?
1.46. Write 0.9 as 0.90 so both numbers have the same number of decimal places, then add column by column. Lining the digits up on the right instead gives 0.65, which is the usual slip.
16.3 + 5.08 = ?
21.38. Write 16.3 as 16.30 so both numbers have the same number of decimal places, then add column by column. Lining the digits up on the right instead gives 6.71, which is the usual slip.
7.52 + 9.8 = ?
17.32. Write 9.8 as 9.80 so both numbers have the same number of decimal places, then add column by column. Lining the digits up on the right instead gives 8.50, which is the usual slip.
24.06 + 7.9 = ?
31.96. Write 7.9 as 7.90 so both numbers have the same number of decimal places, then add column by column. Lining the digits up on the right instead gives 24.85, which is the usual slip.
1.25 + 3.75 = ?
5.00. Both numbers already have two decimal places, so the columns line up.
Find the missing number.
? + 4.35 = 12.10
7.75. A missing addend is a subtraction: 12.10 - 4.35 = 7.75. Line up the decimal points for that too.
Find the missing number.
? + 0.68 = 1.50
0.82. A missing addend is a subtraction: 1.50 - 0.68 = 0.82. Line up the decimal points for that too.
Which setup for 5.4 + 12.76 is lined up correctly?
The one with the decimal points in the same column. They have to line up with each other, not with the last digits. Writing 5.4 with an extra zero on the end does it for you.
Which setup for 9.07 + 3.6 is lined up correctly?
The one with the decimal points in the same column. They have to line up with each other, not with the last digits. Writing 3.6 with an extra zero on the end does it for you.
No buttons on these. Answer out loud, then check.
Why does 6.9 + 2.45 catch so many people out?
Because the two numbers have different numbers of decimal places. If you line up the right-hand edges instead of the decimal points you are really adding 69 and 245, which gives 3.14 rather than 9.35. Writing 6.9 as 6.90 first makes the columns line up on their own.
Is it cheating to write 6.9 as 6.90?
No, they are the same number. A zero on the END of the decimal part adds nothing, it just fills the empty hundredths column so the digits sit where they belong. A zero in front, like 0.69, is a completely different number.
1.25 + 3.75 comes to 5.00. Should you write 5 or 5.00?
Both are correct numbers. In money you write $5.00 because prices always show cents. In a plain calculation 5 is fine. What you must not do is write 5.0 and call it 50.
Estimate 24.06 + 7.9 before adding. Why bother?
24 and 8 is about 32, so an answer near 32 is believable and an answer of 24.85 or 3.19 is not. Estimating first is the quickest way to catch a decimal point in the wrong place.
Want it on paper? Download the free printable worksheet above: twelve practice sums, three word problems, a missing-number challenge and a full answer key.