A car owner buys petrol fir Rs 70, 75 and 80 for 3 successive months. What is the approximately average cost per litre. If he spends Rs 14000, 18000 and 16000 respectively
Answers
Answer:
Let us take variable x for per year spending and rates a, b and c for each year respectively
Quantities would be x/a, x/b and x/c for first, second and third year respectively.
Total quantity x(1/a+1/b+1/c).
Total amount: x+x+x=3x.
Overall rate=3x÷[x(1/a+1/b+1/c]
=3÷(1/a+1/b+1/c)
Interest thing is to note here is it does not depend. on yearly spending (if it is constant).
Reciprocal of overall rate can be written as (1/a+1/b+1//c)/3; average of reciprocals of individual rates.
Wow, overall rate is reciprocal of average of reciprocals.
Now, let us do the calculations:
Reciprocals:1/7.5, 1/8, 1/8.5
10/75, 10/80, 10/85
2/15, 1/8, 2/17
(2 × 17 × 8)/(15 ×8×17), (15 ×17)/(15×8×17), (2×15×8)/(15×17×8)
They add up to
(272+255+240))(255×8)
=767/2040
Average=767÷6120
Reciprocal of average 6120÷767
Approximately equals 7.979
Ans.: 7.979 or we can say 7.98