Number of nickels plus number of dimes equals total number of coins
so
n + d = 40
then they tell us that "there are seven times as many dimes as there are nickels"
this translates to
d = 7n
we then plug that into our first equation
and get
n + 7n = 40
then we solve for n
add like terms
8n = 40
then divide both sides by 8
n = 40/8 = 5
therefore Jimmy has 5 nickels
Answer:

And we can use the following formula:

And replacing the info we got:

Step-by-step explanation:
We define two events for this case A and B. And we know the probability for each individual event given by the problem:


And we want to find the probability that A and B both occurs if A and B are independent events, who menas the following conditions:


And for this special case we want to find this probability:

And we can use the following formula:

And replacing the info we got:

2/6, 3/9, 4/12, 5/15, 6/18 ect.
Hope this helped!