Hello, I need two lots of help - firstly is this Algebra or Probability, and secondly - what is the answer ? I made a start (below) but have reached my limit -------------------------------------------------------------------------------------------------------------- Two pupils were to be chosen at random from a school register to take part in a competition. The probability that both would be boys was one- third. Before the choice could be made however, a decision was taken to include pupils from the register of another school in the ballot for the two places. This other chool had a register of 1,000 pupils, and the chance that the two selected pupils would both be boys was reduced to one-thirteenth. How many pupils are on the register of the first school ? ------------------------------------------------------------------------------------------------------------- So far i have worked out that if the chance of two boys from school A is one third, then the chance of the first picked being a boy is 1/sqrt*3 which is approx 57.7% Therefore school A's breakdown is 57.7% male and 42.2% female Population od school B = 1000 The chance of 2 boys from (school A + 1000) = 1/13 therefore the chance of 2 boys = (A + 1000) = 27.7% therefore the breakdown of (A+1000) = 27.7% male and 72.3% female Many thanks, Angela
First, read what the question wants as an answer. That being, the population of school A. What number gives 2 as 1/3 of that number? 6. The rest of the problem is there only to throw you off. Like in the age old riddle, "There once was a man who was going to Tipperary by train. At the train station he meets a woman with 7 kids who was going to London. Each of the kids had 7 goats.............How many were going to Tipperary?" You have two coins totalling 55 cents. One is not a half dollar coin. What is the other?
Thank you Richard, but - If school A has 6 pupils, then the chance of the first selected being a boy is 3 out of 6 (= 1/2) and then there are only 5 pupils left in the population because one has already been selected and removed. The probability that the first two selected are boys = 1/3 therefore, chance of first two being being boys is (1/2) * (X) = 1/3 therefore the chance of the second selected being a boy (X) = 2/3 And what about the chance of the first two selected pupils being boys from school A + school B (6+1000) being one-thirteenth ? I have to submit this answer by tomorrow but i want to understand it first. Thanks, Angela -------------------------------------------------------------------------------------------------------------- Two pupils were to be chosen at random from a school register to take part in a competition. The probability that both would be boys was one- third. Before the choice could be made however, a decision was taken to include pupils from the register of another school in the ballot for the two places. This other chool had a register of 1,000 pupils, and the chance that the two selected pupils would both be boys was reduced to one-thirteenth. How many pupils are on the register of the first school ?
