Question

Some of the children at a school arrive by car.

Answer 1

Answer:

• 74%

Explanation:

You can build a two-way relative frequency table to represent the data:

These are the columns and rows:

               Car         No car      Total

Boys

Girl

Total

Fill the table

• 30% of the children at the school are boys

             Car         No car      Total

Boys                                       30%

Girl

Total

• 60% of the boys at the school arrive by car

That is 60% of 30% = 0.6 × 30% = 18%

             Car         No car      Total

Boys      18%                         30%

Girls

Total

By difference you can fill the cell of Boy and No car: 30% - 18% = 12%

             Car         No car      Total

Boy       18%           12%         30%

Girl

Total

Also, you know that the grand total is 100%

             Car         No car      Total

Boy       18%           12%         30%

Girl

Total                                     100%

By difference you fill the total of Girls: 100% - 30% = 70%

             Car         No car      Total

Boy       18%           12%         30%

Girl                                         70%

Total                                     100%

• 80% of the girls at the school arrive by car

That is 80% of  70% = 0.8 × 70% = 56%

             Car         No car      Total

Boy       18%           12%         30%

Girl       56%                         70%

Total                                     100%

Now you can finish filling in the whole table calculating the differences:

             Car         No car      Total

Boy       18%           12%         30%

Girl        56%         14%         70%

Total     74%          26%      100%

Having the table completed you can find any relevant probability.

The probability that a child chosen at random from the school arrives by car is the total of the column Car: 74%.

That is because that column represents the percent of boys and girls that that  arrive by car: 18% of the boys, 56% of the girls, and 74% of all the the children.