El número misterioso: soy múltiplo de 3 y de 4 y estoy comprendido entre 30 y 99. El resto de mi división por 5 es 4. ¿Quién soy?

84

Step-by-step explanation:

Let the number be x.

As the number is multiple of 3 and 4, so the number must be a multiple of the lowest common factor (LCM) of 3 and 4.

LCM(3,4)=12

So, the number, x, is a multiple of 12.

All the numbers between 30 and 99, which are multiples of 12 are 36, 48, 60, 72, 84, 96.

When x is divided by 5, the remainder is 4, so the unit digit of the number is 4.

Now, the number between 30 and 99, which is multiple of 12 and having the unit digit 4 is 84.

Hence, the required number is 84.