# CLASS-7CROSS PRODUCT RULE OF PROPORTION

CROSS PRODUCT PROPORTION

Suppose, w, x, y, and z are the 1st, 2nd, 3rd, and 4th terms of the proportion respectively then the equation would be  w : x =  y : z . The 1st & 4th terms are called EXTREMES and the 2nd & 3rd terms are called MEANS.

The term z is considered as a 4th and also called the Fourth Proportional to w, x, y.

1st Term         3rd Term             w              y

So, ------------ = ------------  ;  --------  =  --------

2nd Term         4th Term             x              z

If we multiply both the 1st Term X 4th Term = 3rd Term X 2nd Term ; so, wz = yx

The above process is called the cross product rule.

If four numbers w, x, y, & z are in proportion of which any three is known, we can know the remaining unknown number by using the fact that wz = yx .

If four numbers are in proportion then

We can conclude that, the product of the EXTREMES = the product of the MEANS

The above rule helps us to find any term of proportion if any three are known to us.