Cross Multiplication Sums

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Std III is full of subjective division and multiplication sums as described below. These

kinds of sums can be solved by cross multiplication and this method will be useful when you

grow old.

Division:

If 10 pencils cost Rs. 20.00 how much will 1 pencil cost?

10      20

1        ?(how much)

Answer = 1 x 20

              ----------

                    10

Multiplication:

If 1 pencil cost Rs. 20.00 how much will 10 pencil cost?

1             20

10           ?(how much)

Answer  =     10 x 20

                    ----------

                              1

The mathematical basis of cross multiplication is fractions. If you observe you have 2 sets having similar units.

a/b = c/d here a/b has same units and c/d has same units. We can use this algebra equation to solve for the unknown value.

if c is unknown then c = (a x d) / b

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