Mensah is currently 5 years old. Joyce is thrice as old as Mensah. The problem asks in how many years Joyce will be twice as old as Mensah.

1. Problem Description

Mensah is currently 5 years old. Joyce is thrice as old as Mensah. The problem asks in how many years Joyce will be twice as old as Mensah.

2. Solution Steps

Let $M$ be Mensah's current age and $J$ be Joyce's current age.

We are given that $M = 5$ and $J = 3M = 3 \times 5 = 15$.

Let $x$ be the number of years until Joyce is twice as old as Mensah.

In $x$ years, Mensah's age will be $M + x = 5 + x$.

In $x$ years, Joyce's age will be $J + x = 15 + x$.

We want to find $x$ such that Joyce's age is twice Mensah's age.

Thus, $J + x = 2(M + x)$.

Substituting the given values, we have:

$15 + x = 2(5 + x)$

$15 + x = 10 + 2x$

$15 - 10 = 2x - x$

$5 = x$

So, $x = 5$.

In 5 years, Mensah will be $5 + 5 = 10$ years old, and Joyce will be $15 + 5 = 20$ years old.

Since $20 = 2 \times 10$, Joyce will be twice as old as Mensah in 5 years.

3. Final Answer

C. 5 years