Bob has $3.69 in pennies, dimes, and quarters. The number of pennies is three more than the number of dimes. The number of quarters is twice the number of dimes. How many of each coin does he have?

9 pennies, 6 dimes, 12 quarters.

Step-by-step explanation:

Pennies = $0.01

Dimes = $0.10

Quarters = $0.25

Let x be the number of dimes. Then (x + 3) is the number of pennies and 2x is the number of quarters.

We have x($0.10) + (x + 3)($0.01) + 2x($0.25) = $3.69

x($0.10) + (x + 3)($0.01) + 2x($0.25) = $3.69

$0.1x + $0.01x + $0.03 + $0.5x = $3.69

$0.61x = $3.66

x = 6.

Therefore Bob has 9 pennies, 6 dimes and 12 quarters.

18

Step-by-step explanation:

You can multiply 9 x 2 like normal to get 18. Then you look at the signs. They are both negative, meaning their product is positive, making the answer 18.