$580 laptop/ $40 earned a week = about 14.5 weeks to buy the laptop
You have to pick at least one even factor from the set to make an even product.
There are 3 even numbers to choose from, and we can pick up to 3 additional odd numbers.
For example, if we pick out 1 even number and 2 odd numbers, this can be done in
ways. If we pick out 3 even numbers and 0 odd numbers, this can be done in
way.
The total count is then the sum of all possible selections with at least 1 even number and between 0 and 3 odd numbers.
where we use the binomial identity
Pet show has stations for each animal. There are 5 rabbits, 7 cats, 8 dogs, and 4 hamsters.
1. How many cats need to be added to make the probability 1/2.
For the probability to be 1/2, we need there to be 1 cat for every 2 animals. There are 5+8+4 = 17 other animals besides cats so we need to increase the amount of cats to 17 so that it is 1/2 of the total. We already have 7 so we need 17-7 = 10 more cats.
2. Assume we added the cats. What's the probability of picking a dog?
Since we added the cats, the total number of animals is now 17+17 = 34
There are 8 dogs, so the probability of picking a dog will be 8/34 which will reduce to 8/34 = 4/17 (you will pick 4 dogs every 17 attempts).
3. No more animals added. What is the probability of picking a rabbit or hamster?
Total rabbits and hamsters is 5+4 = 9 so there is a 9/34 chance of picking a rabbit or hamster. (you will pick a rabbit or hamster 9/34 attempts).
4. What is the probability of NOT picking a goldfish?
Be careful here... the question is what is the probability that you won't pick a goldfish? Well there are no goldfish, so there is a 34/34 (100%) chance that you won't pick a goldfish. You will NOT pick a goldfish 34 out of 34 times.
