Solved UPSC CDS/OTA Question
A solved UPSC CDS/OTA PYQ - decoded step-by-step.
Solve it the standard way once - then learn the shortcut.
Rs. 3000 is distributed among p, q and r such that p gets 2/3rdof what q and r together get and r gets ½ of what p and q together get. Find q’s share.
Step-by-Step Solution
The complete worked solution.
Every step explained - no skipped algebra.
Step 1: Let the shares be
P = p
Q = q
R = r Total: p + q + r = 3000
Step 2: Use the first condition
P gets 2/3 of what Q and R together get → p = (2/3)(q + r) Multiply both sides by 3: → 3p = 2q + 2r (Equation 1)
Step 3: Use the second condition
R gets 1/2 of what P and Q together get → r = (1/2)(p + q) Multiply both sides by 2: → 2r = p + q (Equation 2)
Step 4: Solve the system
From Equation 1: 3p = 2q + 2r → p = (2q + 2r)/3 (Equation A)
From Equation 2: 2r = p + q → r = (p + q)/2 (Equation B)
Now plug Equation B into Equation A:
p = (2q + 2 × [(p + q)/2]) / 3 → p = (2q + (p + q)) / 3 → p = (3q + p) / 3
Multiply both sides by 3: 3p = 3q + p → 2p = 3q → p = (3/2)q (Equation C)
Now use Equation 2 again: 2r = p + q → 2r = (3/2)q + q = (5/2)q → r = (5/4)q (Equation D)
Step 5: Total sum
p + q + r = 3000 → (3/2)q + q + (5/4)q = 3000 → Convert all to same denominator (LCM = 4): → (6/4)q + (4/4)q + (5/4)q = 3000 → (15/4)q = 3000 → q = (3000 × 4) / 15 = 12000 / 15 = 800