Question

Петя старше Сережи и тяжелее его на 20 кг. А Сережа - втрое легче Пети. Сколько весит Сережа?

Answer 1

Петя весить 30 кг 
Сережа весить 10 кг

Answer 2

Solution:

Let's solve this step by step.

1. Petya is 20 kg heavier than Seryozha. 2. Seryozha is three times lighter than Petya.

Let's denote Petya's weight as P and Seryozha's weight as S.

From the given information, we can form the following equations: 1. P = S + 20 (Petya is 20 kg heavier than Seryozha) 2. S = (1/3)P (Seryozha is three times lighter than Petya)

Now, we can solve these equations to find the weight of Seryozha.

Calculation:

Using the second equation, we can express Petya's weight in terms of Seryozha's weight: P = 3S

Substitute this expression for P in the first equation: 3S = S + 20

Now, solve for S: 3S - S = 20 2S = 20 S = 10

So, Seryozha weighs 10 kg.

Therefore, Seryozha weighs 10 kg.