In a chest there are some gold coins. Captain takes half the coins. Sally takes a fourth of the coins. There are 3 coins left.
How many coins were in the chest at the start?

There were 12 gold coins in the chest at the start.

Step-by-step explanation:

1. Let's review the information given to us to answer the question correctly:

x = Number of gold coins in a chest

1/2x = Number of gold coins taken by the captain

1/4x = Number of gold coins taken by Sally

3 = Number of gold coins left

2. How many coins were in the chest at the start?

Let's write the following equation to solve for x:

1/2x + 1/4x + 3 = x

2x + x + 12 = 4x (Lowest Common Denominator is 4)

4x - 2x - x = 12 (Like terms)

x = 12

There were 12 gold coins in the chest at the start.

Hope this helps :D

starting with:    

5 + x - 12 = 2x - 7   

5 + x - 12 - x = 2x - 7 - x (subtract x from both sides)   

5 - 12 = x - 7 (combine and cancel x's from both sides)   

5 - 12 + 7 = x - 7 + 7 (add 7 to both sides)   

0 = x (add numbers together on both sides)       

so in order for the equation to be true, x must be 0.   

trying x = -0.5   

5 + x - 12 = 2x - 7 (original equation)   

5 + -0.5 - 12 = 2(-0.5) - 7 (plug in value of x)   

5 + -0.5 - 12 = -1 - 7 (did multiplication)   

-7.5 = -8 (did addition on both sides)       

since -7.5 is obviously not equal to -8, the value of -0.5 for x is wrong.   

trying x = 0   

5 + x - 12 = 2x - 7 (original equation)   

5 + 0 - 12 = 2(0) - 7 (plug in value of x)   

5 + 0 - 12 = 0 - 7 (did multiplication)   

-7 = -7 (did addition on both sides)       

since -7 equals -7, that demonstrates that the value of 0 for x is correct.   

trying x = 1   

5 + x - 12 = 2x - 7 (original equation)   

5 + 1 - 12 = 2(1) - 7 (plug in value of x)   

5 + 1 - 12 = 2 - 7 (did multiplication)   

-6 = -5 (did addition on both sides)       

since -6 is obviously not equal to -5, the value of 1 for x is wrong.

b and c

step-by-step explanation: