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ANJU

· started a discussion

· 1 Months ago

doubt (Question: 103136.0 )

i hv doubt in this question. pls do explain.
distance is asked, so why time 12 hr is not multiplied with the result of ap

Question:
The speed of a car increases by 2 km/hr after every hour. If the distance travelled in the first one hour was 35 km, the total distance travelled in 12 hours was-
Options:
A) 456 km
B) 482 km
C) 552 km
D) 556 km
E) None of these
Solution:
Total distance travelled is 12 hr. 35 + 37 + 39 + …… up to 12hr. 
Now the terms are in AP 
Sn = \(\frac{n}{2}\) [2a + (n – 1)d] 
where n is the number of terms and d is the difference between two terms. 
\(\frac{12}{2}\) [2 × 35 + 11 × 2] 
 = 552 kms.

kanhaiya jha

· commented

· 1 Months ago

yes....you can calculate distance from 1 to 12 hours separately..... and then add all...


we know that, speed= distance/time

The speed of a car increases by 2 km/hr after every hour, so obviously distance also will increase by 2km every hour.

So, in first hours distance given is 35 km,
in second, distance will be 35+2 = 37 km,.....and so on upto 12th hour.

Then add all by applying AP formula.

ANJU

· commented

· 1 Months ago

this is the solution given right?? i want its explanation

kanhaiya jha

· commented

· 1 Months ago

Total distance travelled is 12 hr. 35 + 37 + 39 + …… up to 12hr.
Now the terms are in AP
Sn = n/2 [2a + (n – 1)d]
where n is the number of terms and d is the difference between two terms.
122 [2 × 35 + 11 × 2]
= 552 kms.
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