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X = 6 Clue
JACK IS 28, JOHN IS 21. LET A AND B BE JACK'S AND JOHN'S AGE RESPECTIVELY. SO, A + B = 49 THE DIFFERENCE IN THEIR AGES (A - B), ALWAYS REMAIN THE SAME. "WHEN JACK WAS AS OLD AS JOHN IS NOW" MEANS JACK'S AGE WAS B AND JOHN'S AGE HAD TO BE: B - (A - B) = 2B -A JACK IS NOW TWICE THE AGE, SO: A = 2(2B - A) A = 4B - 2A 3A = 4B SUBSTITUTING (A + B = 49), WE CAN GET B = 21 AND A = 28 THEY ARE 10.5 AND 0.5 YEARS OLD. A COMMON WRONG ANSWER IS 10 AND 1. THIS IS WRONG BECAUSE THE DIFFERENCE IN AGE WOULD BE 9, NOT 10 HIS YOUNGER BROTHER WAS 6. LET HIS AGE BE X, DIMPLE'S AGE BE Y, AND HIS FATHER'S AGE BE Z. THEN Z=3Y, Z=X2, Y=2X. SO 6X=X2 AND X=6 HE IS 16 YEARS OLD. WHEN I WAS 4 YEARS OLD, MY BROTHER WAS 2 YEARS OLD (HALF MY AGE), SO MY BROTHER IS 2 YEARS YOUNGER THAN ME. WHEN I AM 18 YEARS OLD, MY BROTHER WILL BE 16 YEARS OLD AS HE IS 2 YEARS YOUNGER THAN ME