60 ÷ 5 = 12; 12 X 2 = 24; or 2 X 60 = 120; 120 ÷ 5 = 24, etc.
Reduction of Common Fractions to Decimal Fractions: The material for this purpose is similar to that of the circular insets, except that the frame is white and is marked into ten equal parts, and each part is then subdivided into ten. In these subdivisions the little line which marks the five is distinguished from the others by its greater length. Each of the larger divisions is marked respectively with the numbers, 10, 20, 30, 40, 50, 60, 70, 80, 90, and 0. The 0 is at the top and there is a raised radius against which are placed the sectors to be measured.
To reduce a common fraction to a decimal fraction the sector is placed carefully against the raised radius, with the arc touching the circumference of the inset. Where the arc ends there is a number which represents the hundredths corresponding to the sector. For example, if the 1/4 sector is used its arc ends at 25; hence 1/4 equals 0.25.
[Page 275] shows in detail the practical method of using our material to reduce common fractions to decimal fractions. In the upper figure the segments correspond to 1/3, 1/4, and 1/8 of a circle are placed within the circle divided into hundredths. Result:
1/3 + 1/4 + 1/8 = 0.70.
The lower figure shows how the 1/3 sector is placed: 1/3 = 0.33.
If instead we use the 1/5 sector we have: 1/5 = 0.20, etc.
Numerous sectors may be placed within the circle; for example: