Basic Math Work Sheets
Solution for Finding the Perfect Cube Root of a Number Mentally
Solutions for Practice Questions:
Patterns make math easy!
Number
N
Square of
N
Cube of N
N3
Last digit of
N3
Patterns
N & N3
1
1
1&1
1
1
2
4
8
8
2&8
3
9
27
7
3&7
4
16
64
4
4&4
5
25
125
5
5&5
6
36
216
6
6&6
7
49
343
3
7&3
8
64
512
2
8&2
9
81
729
9
9&9
N2
Last three digits
10
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100
1000
000
Created be Ming H. Xu
0 & 000
Page 1
Basic Math Work Sheets
Find the Perfect Cube Root of a Number
Solutions for Practice Questions:
1.
3
√3375 = 15
Step1, Group every three digits starting from right side: 3 375.
Step2, Predict the 1st digit of cube root: Since 13< 3 < 23, the 1st digit is 1.
Step3, Predict the 2nd digit of cube root: The given number ends with 5, so the 2nd
digit of cube root is 5. (See the table on page 1)
2.
3.
3
√4096 = 16
3
√1728 = 12
Step1, Group every three digits starting from right side: 1 728.
Step2, Predict the 1st digit of cube root: Since 13 = 1, the 1st digit is 1.
Step3, Predict the 2nd digit of cube root: The given number ends with 8, so the 2nd
digit of cube root is 2. (See the table on page 1)
4.
5.
6.
3
√9261 = 21
3
√117649 = 49
3
√85184 = 44
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Created be Ming H. Xu
Page 2
Solutions for Practice Questions:
3
√21952 = 28
7.
3
√185193 = 57
8.
Step1, Group every three digits starting from right side: 185 193
Step2, Predict the 1st digit of cube root: Since 53 < 185 < 63, the 1st digit is 5.
Step3, Predict the 2nd digit of cube root: The given number ends with 3, so the 2nd
digit of cube root is 7. (See the table on page 1)
3
√35937 = 33
9.
10.
3
√2197000 = 130
Step1, Group every three digits starting from right side: 2197000
Step2, Predict the 1st digit of cube root: Since 13 < 2 < 23, the 1st digit is 1.
Step3, Predict the 3rd digit of cube root: The given number ends with three zeros, so
3
3
the 3rd digit of cube root is 0. ( √2197000 = √2197 × 1000, and 1000 =103)
Step4, Predict the 2nd digit of cube root: the second group "197" ends with 7, so the
2nd digit of cube root is 3.
11.
12.
3
√753571 = 91
3
√250047 = 63
Academic Success Centre
Created be Ming H. Xu
Page 3