Ron had some pens. 3 8 of them were black coloured, 1 4 of them were red coloured and the rest of them were blue coloured. There were 15 blue pens. How many pens did Ron have?

40 pens

Step-by-step explanation:

Let the total number of pens Ron had be x.

We need to find the fraction of the pen that were blue.

3/8 of them were black and 1/4 of them were red. This means that the fraction of the pens that were blue is:

1 - (3/8 + 1/4) = 1 - 5/8 = 3/8

There were 15 blue pens. This means that 3/8 of x is 15:

3/8 * x = 15

x = 15 * 8/3 = 40 pens

Ron had 40 pens.