MACHINE SHOP CALCULATION - OD1640 - LESSON 2/TASK 2
EXAMPLE
Multiply the expression 3 : 2 by 2.
3:2=6:4
Multiplying
both
terms
by
2
renders
the
expression 6 : 4. Check by dividing 3 by 2 which
renders a ratio of 1.5. In the second expression
dividing 6 by 4 also renders a ratio of 1.5.
Thus, 3 : 2 is equal in value to 6 : 4.
Divide the expression 8 :
4 by 4.
8:4=2:1
Dividing both terms by 4 renders the expression
2 : 1.
Check by dividing 8 by 4 in the first
expression, which renders a ratio of 2. In the
second expression dividing 2 by 1 renders a ratio
of 2. Thus 8 : 4 is equal in value to 2 : 1.
c.
Proportion.
(1) Proportion is a statement of equality between two ratios. Thus, 3 : 4
: : 6 : 8. The symbol (: :) means "as" or "equals." Either this symbol or
the equal sign (=) may be used.
The "extremes' are the first and last
terms. The "means" are the second and third terms.
(2) Rule 1. In proportion, the product of the means equals the product of
the extremes.
EXAMPLE
Therefore, 3 : 4 : : 9 : 12.
4 x 9 = 36
Multiply the means.
3 x 12 = 36
Multiply the extremes.
Thus, the two expressions
are equal.
NOTE: This makes it possible to find an unknown quantity. In other words,
when three terms of a proportion are known the fourth can be found.
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