Of the three numbers, 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) 15 B) 20 C) 25 D) 30 E) 35
Sol.   Let the numbers be x,y and z.   Then, x + y = 45   y+z = 55 and   3x+z = 90   ⇒ y = 45 - x, z = 55 - y = 55 - (45 - x) = 10 + x.   ∴ 3x + 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>D</result>
Of the three numbers, 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