Answer:
25/2907
Explanation:
Probability = Expected outcome/Total outcome of events
If a child's toy train collection contains 5 engines, 5 red cars, 7 blue cars, and 2 cabooses, the total collection will be 5+5+7+2 = 19 total collection
Note that if we are choosing this parts to make part engine, his car parts will no longer be replaced. Hence this is a problem of probability without replacement
If we randomly select pieces to make a three-part train of engine, red car and caboose, this can be chosen in that order and the following ways;
Probability of choosing an engine = 5/19
Probability of choosing a red car = 5/18 (note that the total collection has reduced by 1 since we didn't replace the engine)
Probability of choosing a carboose= 2/17 (the car chosen was not replaced as well)
Therefore the probability of randomly selecting pieces to make a three-part train of engine, red car, caboose is the product of the three probability calculated above i.e 5/19 * 5/18 * 2/17 = 50/5814
= 25/2907