RATIO APPLIED TO SCALE DRAWINGS

Since it is not always possible to make a drawing full size, the size of the drawing maybe made in a given ratio to the full size of the object.

Example:

In the above example, A represents the object in its full size and B represents a drawing one-half size. The ratio of the drawing B to object A is one to two. (1/2) (1:2)

Drawings may be commonly "scaled down" by the use of the following ratios:

Let:

CIRCUMFERENCE RULE

The above illustration shows a portion of a circumference rule. This is an example of the application of a ratio. The upper edge of the rule is graduated in such a manner that one inch on the upper scale is in the ratio of 3.1416 to 1 on the lower scale. This is in the ratio of the circumference of a circle to its diameter, so that any diameter can be converted to a circumference or vice versa by reading directly across the rule.

In sheet metal pattern development, effective use can be made of the circumference rule. By using the circumference side, you can lay out the development of large objects. After making the layout, you can make the development of the pattern full size.

PERCENTAGE

Percentage (%) is a way of expressing the relationship of one number to another. In reality, percentage is a ratio expressed as a fraction in which the denominator is always one hundred.

Example:

The ratio of 6 to 12, expressed as %:

The ratio of 6 to 12 may be expressed as .5 or 1. To change to %, move the decimal two places to the right.

This means there are 50 parts to 100.

From a galvanized iron sheet weighing 46 1/4 pounds, an "ell" and one section of pipe were produced which weighed 30 pounds. Find the percentage of the scrap.

PROPORTION

Proportion is a statement of two ratios which are equal.

SOLVING PROPORTIONS

Given the proportion:

Example:

If 50 sheets of galvanized iron weigh 2,313 pounds, how

CROSS MULTIPLY

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