The standard weight is measured by height (cm)- 105 (kg), so it is just right for girls with height 160- 105=55, that is, 55kg.

Everyone can't grow up to the standard, so there is still 10% floating up and down, from (+10) to (-10), 55 kg × 10% = 5.5, which means that the weight of 50-60kg is normal.

But it also depends on personal circumstances. If you are a sports athlete, your body has a high content of muscle tissue, so you can relax properly. If you exercise less, your fat content will be stricter and your weight will be lower.