One Letter at a Time

● Science 8 · Term 1 · Week 4

Name: Section: Date:

Teacher: For a learner who did not get there with <code>worksheet.html</code>. This is not a shorter version — it starts with two coins in the hand and reaches letters in a grid only in task 3. Four tasks, big boxes, and a worked example above each. Tasks 1 and 2 need two coins per learner.

1 Two coins, twenty times — heads is T, tails is t

Worked example: Flip both coins together. Heads and tails → Tt. Write it in the tally. Flip again.

Result	Tally	How many
TT (two heads)
Tt (one of each)
tt (two tails)

Notice which row filled up fastest. There are two ways to get one of each and only one way to get two heads.

2 Why the middle row is biggest — list every way each result can happen

Worked example: TT: coin 1 heads and coin 2 heads. That is the only way — one way.

Result	Every way it can happen	Number of ways
TT
Tt
tt

3 The same thing, in a grid — this is a Punnett square

Worked example: Put one parent's letters across the top and the other's down the side. Each box takes the letter above it and the letter beside it. Top T + side T = TT.

	T	t
T
t

Compare your four boxes with the three rows in task 1. They are the same four outcomes — and Tt appears twice in both.

4 What it means for one family — read it out loud before writing

Worked example: Three boxes out of four are tall. That means each child has a 3 in 4 chance of being tall. It does not mean three of every four children.

The chance for ONE child

What four children might actually be

This is where <code>worksheet.html</code> Section B begins. When a learner can do task 4 unaided, the bridge is finished.

Answer key — screen only, not printed.
1 · roughly 5 / 10 / 5 in twenty flips, and it varies a lot.  |  2 · TT: heads-heads, one way. Tt: heads-tails and tails-heads, two ways. tt: tails-tails, one way.  |  3 · TT, Tt, Tt, tt.  |  4 · left box: 3 in 4 for each child. Right box: anything from four tall to four semi-dwarf. Task 2 is the one that does the work. A learner who can say why Tt appears twice will never write 1 : 1 : 1 : 1 again.