There are two main laws operating behind an indifference curve being convex to the origin. First is the law of diminishing marginal utility which means as consumer goes on consuming additional units of a particular good the marginal utility derived from one additional unit decreases because the utility or satisfaction achieved starts decreasing and after the point of saturation it becomes negative also...In accordance with this a law called marginal rate of substitution operates simultaneously. For this one should be clear about what it is..Suppose there are two goods X and Y then marginal rate of substitution of X for Y means the no of units of good Y the consumer is willing to forego to get an additional unit of good X given the money income. So it is quite obvious that in order to gain one more unit of good X the no of units of good Y the consumer will be willing to forego will go on diminishing due to the law of diminishing marginal utility..So the indifference curve thus formed will be convex to the origin due to the slope which is determined by marginal rate of substitution.

The relationship between the size of k(multiplier) and MPS( marginal propensity to save) is of an inverse nature.

For ex- 1. Suppose MPS is 0.25 then the size of multiplier will be k = 1/MPS then the ans will be k = 4, which means an investment of Rs. 1 lac will increase the income level by Rs. 4 lacs.                                                                                         If in another case suppose MPS is 0.50 then the size of multiplier will be k = 1/MPS and the ans will be k = 2.

With every increase in MPS, the size of mutiplier falls because saving acts as a leakage in the theory of multiplier.

Economics is a science which helps an individual to fulfill his/her unlimited needs with the use of scarce resources having the art of properly allocating them. it just doesn't mean increase in wealth rather it should be focussed on maximising welfare.

With increase in the price of petrol there will be a decrease in the demand of cars as both petrol and cars are complementary goods..So the demand curve of cars as a result of increase in the price of petrol will be a downward sloped curve.

In indifference curve analysis, a consumer is at equilibrium where marginal rate of substitution(MRS=∆Y/∆X) will be equal to slope of budget line(slope=Px/Py).