Question

From January 1, 2021, the price of petrol (in Rupees per litre) on m^th day of the year is 80 + 0.1 m, where m = 1, 2, 3,..., 100 and thereafter remains constant. On the other hand, the price of diesel (in Rupees per litre) on nth day of 2021 is 69+0-15n for any n. On which date in the year 2021 are the prices of these two fuels equal?

(a) 21st May

(b) 20th May

(c) 19th May

(d) 18th May

Answer 1

Correct option is (b) 20th May

Price of petrol after 100 days = 80 + 0.1 x 100 = 90

Let price of diesel after n^th day = 69 + 0.15 n

69 + 0.15 n = 90 

0.15 n = 90 - 69 = 21

\(\therefore\) n = \(\frac{21}{0.15}\) = 140^th day

140^th day of 2021 = 20^th May 2021.