There are two buildings P and Q. If 15 persons are sent from P to Q, then the number of persons in each building is the same. If 20 persons are sent from Q to P, then the number of persons in P is double the number of persons in Q. How many persons are there in building P?  Choose the correct answer
A) 80	B) 140	C) 120	D) 100	E) 150
Let the number of persons in building P = p   and the number of persons in building Q = q   If 15 persons are sent from P to Q,   then the number of persons in each building is the same   =&gt; p-15 = q+15   =&gt; p - q = 30 ----(Equation 1)   If 20 persons are sent from Q to P,   then the number of persons in P is double the number of persons in Q   =&gt; 2(q - 20) = (p + 20)   =&gt; 2q - 40 = p + 20   =&gt; 2q - p = 60 ----(Equation 2)   (Equation 1) + (Equation 2)=&gt; q = 90   From Equation 1, p = 30 + q = 30 + 90= 
<gadget id="calculator">30 + 90</gadget>
<output>120</output>
120   i.e., Building P has 120 persons   Answer : Option 120
<result>C</result>
There are two buildings P and Q. If 15 persons are sent from P to Q, then the number of persons in each building is the same. If 20 persons are sent from Q to P, then the number of persons in P is double the number of persons in Q. How many persons are there in building P?