Of the three numbers, the sum of the sum of the first two is 45; the sum of the second and the third is 55 and the sum of the third and thrice the first is 90. the third number is :  Options:  A) 20  B) 25  C) 30  D) 3  E) None of these
Solution   Let the numbers be x,y, and z. then, x + y = 45, y + x = 55 and 3 x + z = 90   ⇒ y = 45 - x, z = 55 - y = 55 - (45 - x) = 10 + x.   ∴ 3 x + 10 + x = 90 or x = 20.   y = (45 - 20)= 
<gadget id="calculator">(45 - 20)</gadget>
<output>25</output>
25 and z= (10 + 20)= 
<gadget id="calculator">(10 + 20)</gadget>
<output>30</output>
30.   ∴ third number= 30   Answer 30
<result>C</result>
Of the three numbers, the sum of the sum of the first two is 45; the sum of the second and the third is 55 and the sum of the third and thrice the first is 90. the third number is :