What Is A Cube Number?
A cube number (or perfect cube) is a whole number you get by multiplying a whole number by itself three times: . The small raised is an exponent telling you how many copies of to multiply, which the exponents page explains in general.
The name comes from geometry: unit cubes stack into a solid cube with edge . The live page on cube numbers carries the idea beyond 30.
Three things look alike and are not:
is three copies of added: .
is times itself once: .
is times itself twice: .
The cube of a negative number is negative, since an odd count of negative signs leaves one over: .
How Do You Read The Cubes 1 To 30 Table?
Read the table across: find in the first column, and its cube sits in the last column. For example, the row for shows .
Read it backwards to find a cube root. If a problem gives you , find it in the cube column and read from the same row, so .
The table only lists perfect cubes. A number such as is missing because it sits between and , so its cube root is between and (about ).
Cubes Of 1 To 30 Table
Each table lists the number , its square and its cube , so you can see how much faster cubes grow than squares.
Cubes From 1 To 10
n | n squared | n cubed |
|---|---|---|
1 | 1 | 1 |
2 | 4 | 8 |
3 | 9 | 27 |
4 | 16 | 64 |
5 | 25 | 125 |
6 | 36 | 216 |
7 | 49 | 343 |
8 | 64 | 512 |
9 | 81 | 729 |
10 | 100 | 1,000 |
Cubes From 11 To 20
n | n squared | n cubed |
|---|---|---|
11 | 121 | 1,331 |
12 | 144 | 1,728 |
13 | 169 | 2,197 |
14 | 196 | 2,744 |
15 | 225 | 3,375 |
16 | 256 | 4,096 |
17 | 289 | 4,913 |
18 | 324 | 5,832 |
19 | 361 | 6,859 |
20 | 400 | 8,000 |
Cubes From 21 To 30
n | n squared | n cubed |
|---|---|---|
21 | 441 | 9,261 |
22 | 484 | 10,648 |
23 | 529 | 12,167 |
24 | 576 | 13,824 |
25 | 625 | 15,625 |
26 | 676 | 17,576 |
27 | 729 | 19,683 |
28 | 784 | 21,952 |
29 | 841 | 24,389 |
30 | 900 | 27,000 |
The squares column is the same list you will find on square 1 to 30, and multiplying each square by once more gives the cube beside it.
What Are The Cubes Of Even And Odd Numbers From 1 To 30?
The cubes of the fifteen even numbers are all even, and the cubes of the fifteen odd numbers are all odd. Cubing keeps the factor if it is there and cannot create one if it is not.
Even n | 2 | 4 | 6 | 8 | 10 | 12 | 14 | 16 | 18 | 20 | 22 | 24 | 26 | 28 | 30 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
n cubed | 8 | 64 | 216 | 512 | 1,000 | 1,728 | 2,744 | 4,096 | 5,832 | 8,000 | 10,648 | 13,824 | 17,576 | 21,952 | 27,000 |
Odd n | 1 | 3 | 5 | 7 | 9 | 11 | 13 | 15 | 17 | 19 | 21 | 23 | 25 | 27 | 29 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
n cubed | 1 | 27 | 125 | 343 | 729 | 1,331 | 2,197 | 3,375 | 4,913 | 6,859 | 9,261 | 12,167 | 15,625 | 19,683 | 24,389 |
Every even cube is in fact a multiple of , because . So .
Where Do Cubes 1 To 30 Show Up, And Why Do They Matter?
Cubes 1 to 30 show up whenever you measure the space inside a box with equal sides. A cube-shaped box cm on each side holds cubic centimetres, which is just under litres.
The litre itself is a cube: a box cm on each side holds , exactly one litre. A puzzle cube is built from small cubes, and doubling every side of any box multiplies its volume by , which is why a box twice as wide holds eight times as much.
What Patterns Hide In Cubes 1 To 30?
Five patterns run through the table, and each one lets you rebuild or check a cube instead of recalling it cold.
Last Digits Repeat Every Ten
The last digit of depends only on the last digit of :
Last digit of n | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
|---|---|---|---|---|---|---|---|---|---|---|
Last digit of n cubed | 0 | 1 | 8 | 7 | 4 | 5 | 6 | 3 | 2 | 9 |
Seven digits map to themselves; only the pairs and swap. So ends in and ends in , and you can check either one in a second.
Digital Roots Are Always 1, 8 Or 9
Add the digits of any cube, and keep adding until one digit is left. The result is always , or , in the repeating order as goes
For : , then . Since is a multiple of , the digital root is the expected one, which makes this a fast check on a calculation.
The Gaps Between Cubes Grow Steadily
Consecutive cubes differ by :
The gaps run For the last step in the table, , and as well.
Every Cube Is A Run Of Odd Numbers
Write the odd numbers in order and group them as , then the next two, then the next three. Each group adds up to a cube:
In general is the sum of consecutive odd numbers starting at , so is , thirty odd numbers with total .
Some Cubes Are Also Squares
When is itself a perfect square, is a perfect square too. Inside 1 to 30 that gives five numbers that are both: , , , and .
What Is The Sum Of Cubes From 1 To 30?
The sum of cubes from 1 to 30 is . You do not need to add thirty numbers, because the sum of the first cubes equals the square of the sum of the first whole numbers:
The inner part, , is the triangular number from sum of natural numbers. The proof and more cases are on sum of cubes of n natural numbers.
How Do You Remember Cubes From 1 To 30?
You remember cubes from 1 to 30 best by knowing ten of them well and rebuilding the other twenty from patterns. A chanted list tends to fade, while a method you understand can always be rebuilt.
Anchor on 1 to 10. These ten () are the ones worth knowing on sight, because every later cube is built from them.
Use the decade anchors. , , : the cube of a multiple of ten is the cube of its first digit with three zeros.
Check the last digit. The last-digit table above confirms every answer, and it is right for all thirty.
Step from the nearest anchor. Numbers next to , or come straight from the identity in the next section.
Check with the digital root. If your answer's digital root is not , or , something slipped.
How Do You Calculate A Cube Quickly In Your Head?
You calculate a cube in your head by splitting the number into a round part and a small part, then using the cube identity. The identity is the cube of a binomial:
For , take , :
For , take , with the minus version:
For a number in the middle of a decade, squaring first is often faster: , using . The mental math tricks page collects more splits like this one.
How Do You Find A Cube Root From The Table?
You find the cube root of any perfect cube up to from two clues: its last digit and its size. This is the "cube root 1 to 30 trick" in step-by-step form.
Last digit of the root: Use the last-digit table backwards: a cube ending in has a root ending in , ending in means a root ending in , and so on.
Tens digit of the root: Drop the last three digits of the cube and see which decade cube the rest sits above: to means the root is in the teens, to means the twenties.
Put them together: For : last digit gives ; dropping leaves , which is between and , so the tens digit is . The root is .
Check: . The full list of roots is on cube root 1 to 100.
Examples Of Cubes 1 To 30
Example 1
Find the volume of a cube-shaped box with edge cm.
Final answer:
Example 2
A student finds by writing . Is that right?
Check the size first. must be more than by a lot more than , because one extra unit on every edge adds three whole slabs of volume.
The break is splitting the cube over the plus sign: is not . The two middle terms and went missing.
Final answer: .
Example 3
Which number has a cube of ?
Last digit gives a root ending in . Dropping leaves , between and , so the tens digit is .
Final answer:
Example 4
Find , then the sum of cubes from 11 to 30.
Final answer: and
Readers who add the ten cubes one by one usually land within a few units of and then cannot tell which addition slipped; the square-of-55 route removes that risk entirely.
Example 5
Show that is a sum of two cubes in two different ways, using only the table.
Final answer: both pairs, and , give .
Example 6
How many dice with cm edges fill a cube-shaped box with cm edges?
Each edge holds dice, so the box holds
Check by volume: .
Final answer: dice
What Mistakes Do Students Make With Cubes 1 To 30?
Mistake 1: Multiplying By 3 Instead Of Cubing
Where it slips in: The first week of exponents, when the raised looks like an ordinary factor.
Don't do this: Write .
The correct way: . Students who say "four times four times four" aloud for the first few problems stop confusing the exponent with a multiplier.
Mistake 2: Dropping A Zero On The Decade Cubes
Where it slips in: Cubing , or quickly, when the zeros get counted as two instead of three.
Don't do this: Write .
The correct way: Each factor of brings one zero, and there are three factors: . The rusher who writes has actually computed , the same that appears in the expansion of .
Mistake 3: Swapping The 2 And 8 (Or 3 And 7) Endings
Where it slips in: Checking a cube's last digit from memory, especially for , , and .
Don't do this: Expect to end in , then "correct" a right answer of .
The correct way: Only two pairs swap: and . The second-guesser who doubts a correct is the reader this pair trips most, so check with instead of trusting a hunch.
Where Can You Get Help With Cubes And Mental Maths?
Cubes become automatic once someone has you rebuild them from patterns a few times with feedback. Mental maths for kids practises exactly this kind of quick, pattern-based arithmetic, and a middle school math tutor can connect cubes to volume and exponents.
For learners moving into identities like , an algebra tutor helps, and math classes online give a steady weekly routine.
Conclusion
Cubes 1 to 30 are the thirty perfect cubes from to , with .
Even numbers have even cubes and odd numbers have odd cubes; the last digit and the digital root check any value.
The sum of all thirty is , from the sum-of-cubes formula.
The identity rebuilds any cube near , or in seconds.
The usual errors are writing for , dropping a zero on decade cubes, and swapping the 2 and 8 endings.
Practice These Before Moving On
Find using .
Which number has a cube of ?
Find .
A cube has volume . Find its edge.
Find the difference without working out either cube.
Answers:
(last digit gives ; lies between and )
cm
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