After losing 3 baseball cards, Peter gave half of his remaining cards to Bobby. If Peter gave Bobby 9 baseball cards, how many cards did Peter start with?

Linear equation: 
1
2
(x - 3) = 9

Bobby claims that Peter started with 21 cards. Which statements are true about verifying Bobby’s claim? Check all that apply.
Substitute 21 for x in the original equation.
Substitute any number for x in the original equation.
Bobby’s claim that x = 21 is correct.
The result of verifying Bobby’s work is 9 = 9.
The result of verifying Bobby’s work is 21 = 21.

1 answer

To solve the problem, let's first verify the original equation:

Given: Peter lost 3 baseball cards, so if he started with \( x \) cards, he has \( x - 3 \) cards left. Peter then gave half of his remaining cards to Bobby, which is represented as:

\[ \frac{1}{2}(x - 3) = 9 \]

Now, solving for \( x \):

  1. Multiply both sides by 2: \[ x - 3 = 18 \]

  2. Add 3 to both sides: \[ x = 21 \]

Thus, Peter started with 21 baseball cards.

Now, to verify Bobby's claim that Peter started with 21 cards, we can go through the statements:

  1. Substitute 21 for x in the original equation: True. This verifies whether \( x = 21 \) holds true in the equation.

  2. Substitute any number for x in the original equation: False. This does not verify Bobby's specific claim; it only tests if the equation holds for other values.

  3. Bobby’s claim that x = 21 is correct: True. We determined \( x = 21 \) is indeed correct.

  4. The result of verifying Bobby’s work is 9 = 9: True. When substituting \( x = 21 \) into \(\frac{1}{2}(21 - 3) = 9\), it holds true.

  5. The result of verifying Bobby’s work is 21 = 21: False. This statement doesn't apply to the context of verifying the original equation; instead, we compare numerical outcomes (like checking if both sides of an equation are equal).

So, the true statements about verifying Bobby’s claim are:

  • Substitute 21 for x in the original equation.
  • Bobby’s claim that x = 21 is correct.
  • The result of verifying Bobby’s work is 9 = 9.