The Educational screen (c1922-c1956])

Page 302 The Educational Screen IN AND FOR THE CLASSROOM Conducted by Wilber Emniert Director Visual Education, State Teachers College, Indiana, Pa. Visual Instruction in the Teaching of Percentage By FRIEDA S. HARRELL T^EACHERS of science were among the first lo utilize visual methods of instruction and to con- struct their own materials by diagram or by photog- raphy. The fact is well illustrated by the article, "Lantern Slides of Cellophane" by Webb and Wilson in The Educational Screen for February, 1938. Teachers of the skill subjects, however, have been slow to adapt this medium to their use. Mathematics has particularly neglected it, although it can be used ad- vantageously, even from a time saving standpoint, in many aspects of the subject. Even the bugbear of seventh grade percentage can be at least partially conquered by the use of visual methods. A percentage diagram can form the basis of thought for all problem work. Three slides are suf- ficient, although more can be used. An india ink dia- gram on cellophane can be enclosed between two pieces of glass or simply glued between two 23/2-inch frames of thin cardboard. It could also be drawn directly on one slide glass. If squared paper is placed behind the chosen medium, the diagrams can be made very quickly and three slides can be constructed in fifteen to thirty minutes. For 2" x 2" slides, the diagram can be drawn in while chalk on the blackboard and photo- graphed. The negative of a 35 mm. film, since the black and white of ihe original are reversed, can then be placed between two glasses. The slides are projected in daylight on the black- board, the lines of the slide being blacker than the board. Children at the front corners of the class can be moved back or the front window shade can be drawn Wonderful NEW ~~ Slide Binder for 2" X 2" Glass Slides The new Marshall No. 1 Slide Binder saves time and money and does a better job easier. Takes all size tape I rolls with cores from ' %" to I'/a" diameter. Necessary data for filing may be writ- ten on masks. Priced at only $4.S0 plus postage. Write for complete facts described in our new- est Catalog of Cameras an-t Supplies. This catalog is Free and should save you money. Write for it noiv! 230 S. WABASH, DEPT. 511 CHICAGO, U.S.A. (EST. 1899) ONLY $4.50 Vernon H. Davey Jr. High School, East Orange, N. J. if the diagram is not sufficiently clear. A section of board painted white is useful but not necessary. Reproduction of the three basic diagrams follow. Basic Slides, 1, 2 and 3 When the class have learned that "per cent means hundredths" and that 25/100 equals 34 and 20/100 equals 1/5, etc., they are ready to be introduced to the percentage diagram. Diagram number one is projected on the board and individuals are sent to cut off with chalk a section equal to 25%, 50%, or 75% of the diagram. Other figures can also be introduced: a cir- cle divided into quadrants, an equilateral triangle di- vided into equal sections, a parallelogram without sec- tions which a child can cut into 50% divisions three dif- ferent ways. The class will by this time have ideas of their own for further illustrations. A dozen oranges can be represented by the following diagram. The slowest children can then see 25%, 50%, 75%, 33 1/3%, 66 2/3%, or 16 2/3% of a dozen, by shad- ing in the fraction with CENTRAL CAMERA CO. diagonal lines. The con- cept of a per cent as a fraction is well estab- lished before problem work is begun. A little imagination takes care of such problems as "What per cent of a foot is an inch?" or Figure 1 "What per cent of a yard are six inches?" The contest element can be introduced here by di- viding the class into two equal sections and giving a point for each correct answer. If each contestant calls on the next from the opposing team, it is insured that the dull children will be called on first. It is quite a feather in the dunce's cap, too, if he can get the cor- rect answer, as he often does. While the work is new, the children beg to "keep on with the contest" long after any teacher could hope to get good attention for