Answer:
x + (x-3) = 21
x + x - 3 = 21
2 x - 3 = 21
Step-by-step explanation:
In this problem, let us first analyze the situation. It says here that Geraldo and Yan both had marbles of their own. The problem states that together, they have a total of 21 marbles. However, we know here from the problem that they have different number of marbles each. Geraldo seems to have lesser number of marbles than Yan. Yan have three marbles more than Geraldo.
We can write the equation starting from assigning the unknown.
We'll use x.
x is the number of marbles that Yan have.
if x is Yan's, then, we can say that x-3 is Geraldo's.
Put them together into the equation.
Yan's plus Geraldo's is equal to 21.
Substitute using the represented unknowns.
x + (x-3) = 21.
In solving, we can also rule out that:
x + x - 3 = 21
2 x - 3 = 21
2 x = 21 + 3
2 x = 24
x = 12
x - 3 = 9
Yan has 12 marbles
and Geraldo has 9 marbles.