RRB Group D 22-Sep-2018 Shift 1 Solved Paper

Question : 9 of 100

Marks: +1, -0

If the edge of a cube is increased by

4 \ { cm},

the volume will increase by

988 \ { cm}^{3}

. Then the original length of each edge of the cube is

Solution:

Let edge length is

a

.
Volume

=a^{3}

(a+4)^{3}=a^{3}+988

a^{3}+64+12 a(a+4)

=a^{3}+988

64+12 a^{2}+48 a=988

a^{2}+4 a-77=0

(a+11)(a-7)=0

a=7 \ { cm}

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