model 3 based on positive and negative exponent Practice Questions Answers Test with Solutions & More Shortcuts

Question : 36 [SSC CISF Constable 2011]

If 0.42 × $100^k$ = 42, then the value of k is

a) 2

b) 3

c) 1

d) 4

Answer:(c)

0.42 × $100^k$ = 42

$42/100 × 100^k$ = 42

$100^k={42×100}/42=100^1$

k=1

Question : 37 [SSC DEO 2009]

If $3^{x + y}$ = 81 and $81^{x - y}$ = 3, then the value of x is

a) $15/8$

b) 39

c) $17/8$

d) 42

Answer:(c)

$3^{x + y}$ = 81 and $81^{x - y}$ = 3

$3^{x + y}$= 81

$3^{x + y} = 3^4$

x + y = 4 ...(i)

and $81^{x - y}$ = 3

$(3^4)^{x - y}$ = 3

$3^{4x - 4y} = 3^1$

4x - 4y = 1 ...(ii)

By equation (i) × 4 + (ii) we have,

4x + 4y = 16…(iii)

4x-4y=1…(iv)

Solving these two equations(iii),(iv)

8x=17 ⇒ $x = 17/8$

Question : 38 [SSC CHSL 2015]

The exponential form of $√{ √{2}×√{3}}$ is :

a) $6^{1/2}$

b) $6^{1/4}$

c) $6^{-1/2}$

d) 6

Answer:(b)

Expression = $√{ √{2} × √{3}}$

= $(√2 ×√3)^{1/2}=(2^{1/2} × 3^{1/2})^{1/2$

= $(6)^{1/2× 1/2} = (6)^{1/4}$

IMPORTANT quantitative aptitude EXERCISES

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