[The narrator reads out the onscreen text.]

NARRATOR: The 330 subjects volunteering for a medical study are classified by sex and blood pressure level, measured as high, normal or low. Complete the two-way table below.

[The three rows of the table are labelled "Male", "Female" and "Total". The four columns of the table are labelled "High", "Normal", "Low" and Total". Figures in the table show that: 176 males have high blood pressure, a total of 168 people have high blood pressure, 44 males have normal blood pressure, 24 females have low blood pressure, a total of 44 people have low blood pressure and that a total of 240 males and 90 females were interviewed - 330 people in total. The other spaces in the table are blank.]

NARRATOR: If we know three pieces of information in any row, we can complete that row. If we know two pieces of information in any column, we can complete that column. Consider row one in which we know three pieces of information. There are 240 males in total, 176 of whom have high blood pressure and 44 of whom have normal blood pressure. So we can calculate the number of males with low blood pressure by subtracting 176 and 44 from 240.

[240 - 176 - 44 = 20. The number 20 is written in the box showing males with low blood pressure.]

NARRATOR: Consider column one in which we know two pieces of information. There are 198 subjects with high blood pressure, 176 of whom are male. So the number of females with high blood pressure can be calculated by subtracting 176 from 198.

[198 - 76 = 22. The number 22 is written in the box showing females with high blood pressure.]

NARRATOR: Consider row two in which we know three pieces of information. There are 90 females in total, 22 of whom have high blood pressure and 24 of whom have low blood pressure. We can calculate the number of females with normal blood pressure by subtracting 22 and 24 from 90.

[90 - 22 - 24 = 44. The number 44 is written in the box showing females with normal blood pressure.]

NARRATOR: Consider column two in which we now know two pieces of information. There are 44 males with normal blood pressure and 44 females with normal blood pressure, which gives a total of 44 plus 44, so 88 people who have normal blood pressure.

[The number 88 is written in the box showing the total number of people with normal blood pressure.]

NARRATOR: The two-way table is now complete.