John bought some stamps. He used 3/5 of then to mail letters. He had 12 stamps left. How many stamps did he use?

So 2/5 of the stamps are left with 12 stamps. So there for 1/5 of the stamps is 6 stamps. Now just multiply 6*3 for the amount that he sent.

=18

18

To find out how many stamps John used, we can first calculate the total number of stamps he initially had.

Let's assume the initial number of stamps John had is represented by the variable "x".

According to the problem, John used 3/5 of the stamps to mail letters. This means he used (3/5) * x stamps.

We also know that he had 12 stamps left after using some of them. So, we can write the equation:

x - (3/5) * x = 12

To solve this equation, we can simplify it as follows:

(2/5) * x = 12

Next, we can isolate the variable x by multiplying both sides of the equation by the reciprocal of (2/5), which is (5/2):

x = 12 * (5/2)

Simplifying further, we have:

x = 60/2

x = 30

Therefore, John initially had 30 stamps.

To find out how many stamps he used, we can substitute this value into the equation:

(3/5) * x = (3/5) * 30

This simplifies to:

(3/5) * 30 = 18

Therefore, John used 18 stamps to mail letters.

To find out how many stamps John used, we need to subtract the number of stamps he had left from the total number of stamps he originally bought.

Let's denote the total number of stamps John bought as "x."

We know that he used 3/5 of the stamps to mail letters, which means he had 2/5 of the stamps left.

We can set up an equation to represent this information: (2/5)x = 12.

To solve for x, we can multiply both sides of the equation by the reciprocal of 2/5, which is 5/2.

(2/5)x * (5/2) = 12 * (5/2).

Simplifying further, we get: x = (12 * 5) / 2.

By evaluating the expression, we find that x = 30.

Thus, John originally bought 30 stamps, and since he had 12 stamps left, he used 30 - 12 = 18 stamps to mail letters.