Question

1. A box of 80 coins, consisting of only nickels and dimes, is worth 7 dollars and 80 cents. Find the number of nickels.

2. Two drivers are 420 miles away from each other when they started moving towards each other. They meet after 4 hours. What is the speed of the first car, if the second car's speed is 45 mph?

Answer 1

1. 4 nickels
2. 60 mph

Explanation:

1. If all were dimes, the value would be $8.00. The value is actually $0.20 less than that. Replacing a dime by a nickel decreases the value by $0.05, so there must be $0.20/$0.05 = 4 nickels.

2. The total of the two speeds is the rate of closure: (420 mi)/(4 h) = 105 mi/h. The speed of the second car is found by subtracting the speed of the first car from this total:

105 mph - 45 mph = 60 mph