5 yrs

5 yrs ago, the average age of Rasmi and Suravi was 20 yr. Now, the average age of Rasmi, Suravi and Mita is 30 yrs. What will be the age of Mita after 15 years?

Correct answer:

x =  55

Step-by-step explanation:

$$\begin{gathered} \frac{r-5+s-5}{2}=20 \\ \frac{r+s+m}{3}=30 \\ r+s-10=2\cdot 20 \\ r+s=50 \\ \frac{r+s+m}{3}=30 \\ \frac{50+m}{3}=30 \\ 50+m=30\cdot 3 \\ m=90-50=40 \\ x=m+15=40+15=55 \end{gathered}$$

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