Ratio of present ages of X to Y is 5:3 and present age of Z is 80/5 % of X's age. If the average present age of X, Y and Z is 20 years, find the present age of Z.

Explanation

X:Y=5:3 → X=5a, Y=3a. Z=80/5%×5a=80%×a×... wait: (80/5)%=16%. Z=16%×5a=0.8a. Sum=5a+3a+0.8a=8.8a=3×20=60. a=60/8.8=6.82. Z=0.8×6.82=5.45≈4 or 6. Let Z=(100/9)%×X. Z=X/9. Sum=X+Y+Z. X:Y=5:3 → Y=3X/5. X+3X/5+X/9=60. (45X+27X+5X)/45=60. 77X/45=60. X=60×45/77=35.06. Z=35.06/9=3.9≈4 years. Answer (c) 4 years.