Practice MCQ Questions and Answer on Square Root and Cube Root

11.

If the product of four consecutive natural numbers increased by a natural number p, is a perfect square, then the value of p is = ?

• (A) 1
• (B) 2
• (C) 4
• (D) 8

Show Answer

 $$\eqalign{ & {\text{We have,}} \cr & 1 \times 2 \times 3 \times 4 = 24 \cr & {\text{And }}24 + 1 = 25\left[ {25 = {5^2}} \right] \cr & 2 \times 3 \times 4 \times 5 = 120{\text{ }} \cr & {\text{And 1}}20 + 1 = 121\left[ {121 = {{11}^2}} \right] \cr & 3 \times 4 \times 5 \times 6 = 360{\text{ }} \cr & {\text{And }}360 + 1 = 361\left[ {361 = {{19}^2}} \right] \cr & 4 \times 5 \times 6 \times 7 = 840{\text{ }} \cr & {\text{And }}840 + 1 = 841\left[ {841 = {{29}^2}} \right] \cr & \therefore p = 1 \cr} $$

12.

The cube root of .000216 is:

• (A) .6
• (B) .06
• (C) 77
• (D) 87

Show Answer

 $$\eqalign{ & {\left( {.000216} \right)^{\frac{1}{3}}} = {\left( {\frac{{216}}{{{{10}^6}}}} \right)^{\frac{1}{3}}} \cr & = {\left( {\frac{{6 \times 6 \times 6}}{{{{10}^2} \times {{10}^2} \times {{10}^2}}}} \right)^{\frac{1}{3}}} \cr & = \frac{6}{{{{10}^2}}} \cr & = \frac{6}{{100}} \cr & = 0.06 \cr} $$

13.

One-fourth of a herd of camels was seen in the forest. Twice the square root of the herd had gone to mountains and the remaining 15 camels were seen on the bank of a river. Find the total number of camels ?

• (A) 32
• (B) 34
• (C) 35
• (D) 36

Show Answer

 Let the total number of camels be x Then, $$\eqalign{ & \Leftrightarrow x - \left( {\frac{x}{4} + 2\sqrt x } \right) = 15 \cr & \Leftrightarrow \frac{{3x}}{4} - 2\sqrt x = 15 \cr & \Leftrightarrow 3x - 8\sqrt x = 60 \cr & \Leftrightarrow 8\sqrt x = 3x - 60 \cr & \Leftrightarrow 64x = {\left( {3x - 60} \right)^2} \cr & \Leftrightarrow 64x = 9{x^2} + 3600 - 360x \cr & \Leftrightarrow 9{x^2} - 424x + 3600 = 0 \cr & \Leftrightarrow 9{x^2} - 324x - 100x + 3600 = 0 \cr & \Leftrightarrow 9x\left( {x - 36} \right) - 100\left( {x - 36} \right) = 0 \cr & \Leftrightarrow \left( {x - 36} \right)\left( {9x - 100} \right) = 0 \cr & \Leftrightarrow x = 36\,\,\,\,\,\,\,\,\,\,\,\,\left[ {\because x \ne \frac{{100}}{9}} \right] \cr} $$

14.

One-fourth of the sum of prime numbers, greater than 4 but less than 16, is the square of = ?

• (A) 3
• (B) 4
• (C) 5
• (D) 7

Show Answer

 Sum of prime numbers greater than 4 but less than 16 $$\eqalign{ & = \left( {5 + 7 + 11 + 13} \right) \cr & = 36 \cr & \therefore \frac{1}{4} \times 36 \cr & = 9 \cr & = {3^2} \cr} $$

15.

If $$\sqrt{6}=2.449\text{,}$$   then the value of $$\frac{3\sqrt{2}}{2\sqrt{3}}$$   is = ?

• (A) 0.6122
• (B) 0.8163
• (C) 1.223
• (D) 1.2245

Show Answer

 $$\eqalign{ & = \frac{{3\sqrt 2 }}{{2\sqrt 3 }} \cr & = \frac{{3\sqrt 2 }}{{2\sqrt 3 }} \times \frac{{\sqrt 3 }}{{\sqrt 3 }} \cr & = \frac{{3\sqrt 6 }}{{2 \times 3}} \cr & = \frac{{\sqrt 6 }}{2} \cr & = \frac{{2.449}}{2} \cr & = 1.2245 \cr} $$

16.

Which number should replace both the question marks in the following equation ?
$$\frac{?}{1776}=\frac{111}{?}$$

• (A) 343
• (B) 414
• (C) 644
• (D) 543

Show Answer

Answer & Solution Answer: Option E Solution: $$\eqalign{ & {\text{Let }}\frac{x}{{1776}} = \frac{{111}}{x} \cr & {\text{Then, }} \cr & \Leftrightarrow {x^2} = 111 \times 1776 \cr & \Leftrightarrow {x^2} = 111 \times 111 \times 16 \cr & \Leftrightarrow x = \sqrt {{{\left( {111} \right)}^2} \times {{\left( 4 \right)}^2}} \cr & \Leftrightarrow x = 111 \times 4 \cr & \Leftrightarrow x = 444 \cr} $$

17.

If $$\sqrt{33}=5.745\text{,}$$   then which of the following values is approximately $$\sqrt{\frac{3}{11}}\text{ ?}$$

• (A) 1
• (B) 6.32
• (C) 0.5223
• (D) 2.035

Show Answer

 $$\eqalign{ & = \sqrt {\frac{3}{{11}}} \cr & = \sqrt {\frac{{3 \times 11}}{{11 \times 11}}} \cr & = \frac{{\sqrt {33} }}{{11}} \cr & = \frac{{5.745}}{{11}} \cr & = 0.5223 \cr} $$

18.

The square root of $$\left(7+3\sqrt{5}\right)$$  $$\left(7-3\sqrt{5}\right)$$   is

• (A) $$\sqrt{5}$$
• (B) 2
• (C) 4
• (D) $$3\sqrt{5}$$

Show Answer

 $$\eqalign{ & \sqrt {\left( {7 + 3\sqrt 5 } \right)\left( {7 - 3\sqrt 5 } \right)} \cr & = \sqrt {{{\left( 7 \right)}^2} - {{\left( {3\sqrt 5 } \right)}^2}} \cr & = \sqrt {49 - 45} \cr & = \sqrt 4 \cr & = 2 \cr} $$

19.

The least perfect square number divisible by 3, 4, 5, 6 and 8 is = ?

• (A) 900
• (B) 1200
• (C) 2500
• (D) 3600

Show Answer

 L.C.M. of 3, 4, 5, 6, 8 is 120 Now 120 = 2 × 2 × 2 × 3 × 5 To make it a perfect square, it must be multiplied by 2 × 3 × 5 So, required number $$\eqalign{ & = {2^2} \times {2^2} \times {3^2} \times {5^2} \cr & = 3600 \cr} $$

20.

R is a positive number. It is multiplied by 8 and then squared. The square is now divided by 4 and the square root is taken. The result of the square root is Q. What is the value of Q ?

• (A) 3R
• (B) 4R
• (C) 7R
• (D) 9R

Show Answer

 $$\eqalign{ & \Rightarrow {\text{Q}} = \sqrt {\frac{{{{\left( {8{\text{R}}} \right)}^2}}}{4}} \cr & \Rightarrow {\text{Q}} = \frac{{\sqrt {{{\left( {8{\text{R}}} \right)}^2}} }}{{\sqrt 4 }} \cr & \Rightarrow {\text{Q}} = \frac{{8{\text{R}}}}{2} \cr & \Rightarrow {\text{Q}} = 4{\text{R}} \cr} $$