Yes No Total
Children 0.3 0.4 0.7
Adults 0.25 x 0.3
Total 0.55 0.45 1
We note that x is given in the row "Adults" and in the column "No".
We can then obtain the value of x by subtracticg the column total by the known value in the column (of subtracticg the row total by the known value in the row).
Let us consider the column "No". We note that the column total is 0.45 (given at the bottom of the column), while the other known value in the table is 0.4