Question
The speed of a bike increases by 3 km/hr after every 1
hour. If the distance travelled by the bike in 1st hour is 25 km, the find the total distance travelled by the bike in 20 hours.Solution
Since, the speed of the bike increases by 3 km/hr after every 1 hour, therefore the bike will travel 3 km extra after every 1 hour. Therefore, distance travelled by the bike in 1st hour = 25 km Distance travelled by the bike in 2nd hour = 25 + 3 = 28 km Distance travelled by the bike in 3rd hour = 28 + 3 = 31 km This form an AP i.e. 25, 28, 31………distance travelled in 20th hour Therefore, total distance travelled by the bike in 20 hours = sum of the AP Distance travelled in 20 hours = (n/2){2a + (n – 1)d} Where n = number of terms = 20, a = 1st term = 25 and d = common difference = 3 Therefore, distance travelled in 20 hours = (20/2){2 × 25 + (20 – 1) × 3} = (20/2)(50 + 57) = 1070 km
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