it depends, what level of problem are you looking for?
Level 1
Marta has some marbles. Martina has 2time as much as Marta has. if they together have 30, how many does each of them has?
Level 2
Marta , Martina, Martin have marbles, each of them have marbles of one color. Marta has green, Martina has blue, Martin has red. Martina has 2 times what Marta has and Martin has half as much as Marta. If they mixed them all together in a box and randomly picked one, what's the probability that the marble is one of:
Martas
Martinas
Martins?
Level 3
A triangle ABC has C=90 degree
From C is build HC the high on AB
If AH-HB is equal to the lenght of CA or CB , how big are angle A and B?