Question

The cost of petrol rises by 2 cents a liter. last week a man bought 20 liters at the old price. This week he bought 10 liters at the new price. Altogether, the petrol costs $9.20. What was the old price for 1 liter?

Answer 1

here there is bit ambiguity in the question they didnt mention whether the raise is per day or per week. iam  gng to solve this by taking per week


let the cost of one litre be   X$
the new cost of one litre will be X$+ 2cents              (2 censt =0.02$)
                                               =. (X+.02)$

cost incurred in last week  =  (cost per one liter last week)*(no of litres)
                                             = (X)*(20)  
                                             =  20X


cost incurred in this week  =  (c0st per one litre this week)*(no of litres)
                                             = (X+0.02)*(10)
                                              = 10X+0.2

NOW TOTAL cost incurred  is 10X+0.2+20X =30X+0.2  =9.20
                                               this implies  30X =9
                                                                        X=0.3
 so the old price of petrol for 1 liter  is  0.3 $  or  30 cents