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CBSE Class 9 Answered

A man covered a distance of 3990 km partly by air, partly by sea and the remaining by land. the time spent in air, on sea and on land is in the ratio 1:16:2 and the ratio of average speed is 20:1:3 respectively. if totaln average speed is 42km/hr then the distance covered by sea is_______ A) 1602 KMS B) 1520 KMS C) 1620 KMS D) 1500 KMS
Asked by adalroshan2464 | 28 Nov, 2018, 05:04: PM
Expert Answer
Let the ratio of actual time spent in air, by sea and on land = t : 16t : 2t
 
total time = t + 16t +2t = 19t
 
overall average speed  = begin mathsize 12px style fraction numerator t o t a l space d i s tan e over denominator t o t a l space t i m e end fraction space equals space fraction numerator 3990 over denominator 19 t end fraction end style....................(1)
 
from eqn.(1), we get t = 5hrs ;
Hence time spent on air = 5 hr ; time spent by sea = 16×5 = 80 hr ; time spent on land = 2×5 = 10 hr .
 
Let the ratio of actual speed in air, on sea and on land = 20v : v : 3v
 
distance covered in air = 20v×5 = 100v km
distance covered on sea = v×80 = 80v km
distance covered on land = 3v×10 = 30v km
 
total distance 100v+80v+30v = 210v = 3990 km ........................(2)
 
from (2) we get v = 19 km/hr
 
distance covered by sea = 80×19 = 1520 km
 
Answered by Thiyagarajan K | 29 Nov, 2018, 07:24: AM

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