The speed of a car increases by 2 km after every one hour. If the distance travelled in the first one hour was 30 km, what was the total distance travelled in 10 hours?

Question: The speed of a car increases by 2 km after every one hour. If the distance travelled in the first one hour was 30 km, what was the total distance travelled in 10 hours?

Solution:
Total distance travelled in 10 hours =( 30 + 32 + 34 +...... upto 10 terms)
This is an A.P with first term, a = 30 ,
number of terms, n = 10
d = 2

Required distance = (10/2)[(2 × 30) + {(10 - 1) × 2}] km
= 5 (60 + 18) km
= (5 × 78) km
= 390 km