Question

The sum of a number and it's reciprocal is 21/30. Find the number.

Answer 1

Let the number be X.

Reciprocal of X = ( 1/X ).

Given : Sum of number + Reciprocal of number = 21/30

=> X + 1/X = 21/30

=> X² + 1 / X = 21/30

=> 30 ( X² + 1 ) = 21X

=> 30X² + 30 = 21X

=> 30X² - 21X + 30 = 0

=> 3( 10X² - 7X + 10 ) = 0

=> 10X² - 7X + 10 = 0

X = -b + √B²-4ac / 2a



X = -(-7) + √(-7)² -4×10×10/2×10


X = 7 + √-351/20

Answer 2

Given: Sum of a number and its reciprocal is 21/30.

To find: The number.

Answer:

Let us take the number as x.

Therefore its reciprocal will be 1/x.

Sum of the number and its reciprocal ⇒ x + 1/x

x + 1/x = 21/30

30(x + 1) = 21x

30x + 30 = 21x

30x - 21x = -30

9x = -30

x = -30/9

x = -3.3

Hope it helps :)