Step-by-step Answer:
There is a total of 10 coins, 5 dimes, 2 quarters and three pennies.
By picking a coin, it could be any that shows up out of the 10, so the probability of picking any coin in particular is 1 / 10.
If there are 5 dimes, the probability of picking ANY one particular dime is 1/10, so with 5, the probability of picking ANY of the five dimes is 5/10 = 1/2.
Going along the same line of thought, the probability of picking any of quarters and pennies would be 2/10+3/10 = 5/10 = 1/2 as well.