Question
The speed of a bike increases by 4 km/hr after every 1
hour. If the distance travelled by the bike in 1st hour is 16 km, the find the total distance travelled by the bike in 18 hours.Solution
Since, the speed of the bike increases by 4 km/hr after every 1 hour, therefore the bike will travel 4 km extra after every 1 hour. Therefore, distance travelled by the bike in 1st hour = 16 km Distance travelled by the bike in 2nd hour = 16 + 4 = 20 km Distance travelled by the bike in 3rd hour = 20 + 4 = 24 km This form an AP i.e. 16, 20, 24………distance travelled in 18th hour Therefore, total distance travelled by the bike in 18 hours = sum of the AP Distance travelled in 18 hours = (n/2){2a + (n – 1)d} Where n = number of terms = 18, a = 1st term = 16 and d = common difference = 4 Therefore, distance travelled in 18 hours = (18/2){2 × 16 + (18 – 1) × 4} = (18/2)(32 + 68) = 900 km
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