Cut several disks into thirds and have children practice on cutting, so
that they will be able to make the three parts of each disk equal.
Frequently children will find pleasure in “teaching” one another.
[Illustration]
Then proceed like this: What do you call each of these parts? Why are
they called thirds? How many thirds in a circle? I am going to take a
circle and cut it any way, so as to make three parts; do I call these
unequal parts thirds? Why not? Let me write one-third on a piece of
paper for you. (Write, 1/3.) Draw a circle for me. Instead of cutting
it, draw lines where you would cut it to make thirds. Write one-third
(1/3) on each third of a circle. I write this (1/3 + 1/3). Who can tell
me what the answer is? Are two-thirds and two-thirds more than one? How
much more? I have two-thirds of an apple and give Mary one-third, how
much have I left? Who can give other story problems about thirds?
Everybody try, etc.
Learn sixths along with thirds. Use disks, dots, marks, sticks, and
inches to illustrate.
Remember that no advance should be made until each little part is
understood. Then have fifths compared with fourths, thirds, and halves.
Teach tenths along with fifths.
When twelfths are taught, show the relations between twelfths and
sixths, fourths, thirds, and halves.