# Thread: Need Help in Basic maths

1. ## Need Help in Basic maths

There are few Questions about Percentage and Average that need to solve and would like to know general formula's to solve such questions.Questions are:
Q:1: If the price of petrol be raised by 12.5%, find by what percentage should a consumer decrease the consumption of petrol so that there is no change in his monthly expenditure on petrol?

Q:2: In an examination 80% of the students passed in Maths and 70% passed in English while 10% of the students failed in both the subjects.If 360 students passed in both the subjects, find the total number of students who appeared in the examination?

Q3: As rise of 20% in the price of refined groundnuts oil a family is forced to buy i kg less for $180.Find the original price of refined groundnut oil per kg. Q:4: Nine students of a class contribute a certain sum. Seven of them give$5 each and the other two give $5 and$9 more than the average contribution of the class of 9 students is?

Q:5: A batsman has a certain average of runs for 11 innings. In the 12th inning he scores 129 runs, thereby increasing his average by 9 runs. What is his average for the first 11 innings?

2. There aren't general formulae for problems like this. You just have to think about them. Do you know how to find a percentage of a quantity?

Now there are general formulae for some of the specific quantities that may arise in problems. For example, the general formula for the average of a set of quantities $a_1,a_2,a_3....a_n$ is just:

$Average=\frac{a_1,a_2,a_3....a_n}{n}$