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ramesh bairwa

· started a discussion

· 1 Months ago

a (Question: 220258.0 )

solution?

Question:
A car starts running with the initial speed of 40 km/hr with its speed increasing every hour by 5 km/hr. How many hours will it take to cover a distance of 385 km ?
Options:
A) 8 \(\cfrac{1}{2}\) hours 
B) 9 \(\cfrac{1}{2}\) hours 
C) 9 hours 
D) 7 hours 
Solution:
Ans: (d) Total distance travelled= 385 km 

Distance travelled in 1st hour

= 40 km

Distance travelled in 2nd hour

= 45 km

ATQ,

45 + 45 + .... = 385

\(\cfrac{n}{2}\) [2 × 40 + (n –1)5] = 385

n[80 + 5n – 5] = 770

n(n + 15) = 154

n2 + 15n – 154 = 0

(n + 22) (n – 7) = 0

n = 7

Total time taken = 7 hours

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