We have a jar of coins, all pennies and dimes. All together, we have 309 coins, and the total value of all coins in the jar is $ 19.2. How many pennies are there in the jar?

There are 130 pennies in the jarStep-by-step explanation:We have a jar of coinsAll coins are pennies and dimesThere are 309 coins in the jarThe total value of all coins in the jar is $ 19.2We need to find the number of pennies in the jarAssume that there are p pennies and d dimes in the jar∵ There are p pennies and d dimes in the jar∵ There are 309 coins in the jar∵ All the coins in the jar are pennies and dimes∴ p + d = 309 ⇒ (1)∵ The total value of all coins in the jar is $ 19.2∵ $1 = 100 cents∴ $19.2 = 19.2 × 100 = 1920 cents∵ 1 penny = 1 cent∵ 1 dime = 10 cents∴ p + 10 d = 1920 ⇒ (2)Now we have system of equations, we can solve them to find p∵ p + d = 309 ⇒ (1)∵ p + 10 d = 1920 ⇒ (2)- Multiply equation (1) by -10 to eliminate d∵ (-10)(p) + (-10)(d) = (-10)(309)∴ -10 p - 10 d = -3090 ⇒ (3)Add equations (2) , (3)∴ -9 p = -1170- Divide both sides by -9∴ p = 130There are 130 pennies in the jarLearn more:You can learn more about the system of equations in brainly.com/question/3739260#LearnwithBrainly