Q1: What can be general formula to find cube of any number?
(a) (a±b)3
(b) a2
(c) (a±b)2
(d) b
Ans: (a)
The general formula of finding square of any number is (a±b)3. We need to express the given number whose cube needs to be found in the form of (a±b). We can then use the formula:
(a±b)3= a3 ± 3a2 b+3ab2 ± b3.
Q2: What form can be used to find cube of 13?
(a) (10+3)3
(b) (10-3)3
(c) (10+3)
(d) (10-3)
Ans: (a)
The number 13 can be represented in form 10 + 3, this will help us to calculate the cube of the number. This method would help us eliminate the traditional method of multiplying the number with itself.
Q3: 893 = ____
(a) (90-1)2
(b) (90-1)3
(c) 12
(d) 92
Ans: (b)
If we must find the cube of the 89, we use the second variation i.e.(90-1)3. This would help us and make the calculations easier instead of multiplying the number with itself thrice.
Therefore (90-1)3 = 903 – 3 × 902 × 1 + 3 × 90 × 12 – 13
Therefore (90-1)3 = 729000 – 24300 + 270 – 1
Therefore (90-1)3 = 704969.
Q4: Find the cube of 32.
(a) 32768
(b) 37968
(c) 32769
(d) 35937
Ans: (a)
To find cube of 32, we would use the form
Therefore (30+2)3 = 303 + 3 × 302 × 2 + 3 × 30 × 22 + 23
Therefore (30+2)3 = 27000 + 5400 + 360 + 8
Therefore (30+2)3 = 32768
Q5: Calculate the cube of 201.
(a) 8120604
(b) 8120609
(c) 8120600
(d) 8120601
Ans: (d)
In the multiple-choice question, we can eliminate three options by mere observation. The unit place of cube of 201 should be 1. The only option which has 1 in unit place is 8120601. The other options are incorrect by mere observation.
Q6: 343 = _____
(a) 39504
(b) 39304
(c) 35304
(d) 34304
Ans: (b)
In order to calculate the cube of 34 we use the formula,
(a+b)3, where we consider a=30 and b=4
Therefore (30+4)3 = 303 + 3×302 × 4 + 3 × 30 × 42 + 43
Therefore (30+4)3 = 27000 + 10800 + 1440 + 64
Therefore (30+4)3 = 39304.
Q7: Which of below is not a perfect cube?
(a) 125
(b) 728
(c) 729
(d) 64
Ans: (b)
Perfect cube is formed when a natural number is multiplied to itself thrice. For example, 4 is a natural number which multiplied with itself thrice gives us 64. Hence, 64 is a perfect cube. But we do not have a natural number which multiplied with itself thrice gives us 728. Hence, 728 is not a perfect cube.
Q8: How many perfect cubes exist between 1 and 100?
(a) 4
(b) 20
(c) 16
(d) 8
Ans: (a)
Perfect cube is formed when a natural number is multiplied to itself thrice. There are 4 perfect cubes between 1 and 100. They are 1, 8, 27, 64.
Q9: How many perfect cubes exist between 1 and 1000?
(a) 5
(b) 20
(c) 10
(d) 15
Ans: (a)
Perfect cube is formed when a natural number is multiplied to itself thrice. There are 10 perfect cubes between 1 and 1000. They are 1, 8, 27, 64, 125, 216, 343, 512, 729 and 1000.
Q10: 573 = _____
(a) 193753
(b) 176452
(c) 185193
(d) 186743
Ans: (c)
In order to calculate the cube of 57 we use the formula,
(a-b)3, where we consider a=60 and b=3
Therefore (60-3)3 = 603 – 3 × 602 × 3 + 3 × 60 × 32 – 33
Therefore (60-3)3 = 216000 – 32400 + 1620 – 27
Therefore (60-3)3 = 185193.
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1. What is a cube root? |
2. How do you find the cube of a number? |
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