NIELIT 2019 Feb Scientist D - Section C: 29

Question

Of the three numbers, the sum of the first two is $45$; the sum of the second and third is $55$ and the sum of the third and thrice the first is $90$. The third number is :

• A. $20$
• B. $25$
• C. $30$
• D. $35$

Answer 1

$\text{Let the first number is x, the second number is y & the third number is z}$

$\text{According to  the question}$

$x+y=45   ...(1)$

$y+z=55    ...(2)$

$z+3x=90...(3)$

from (1) & (2)

$x-z=-10...(4)$

from (3) & (4):

$x=20$

from equation (1):

$y=25$

from equation (3):

$z=30$

So option $(C)$ is correct.