Let $5x$ be the number of apples, $2x$ be the number of mangoes, and $y$ be the number of oranges. The total number of fruits is:
$5x + 2x + y = 187$, which simplifies to $7x + y = 187$ (Equation 1).
After selling, the remaining fruits are: apples ($5x - 75$), mangoes ($2x - 26$), and oranges ($\frac{y}{2}$). The ratio of unsold apples to unsold oranges is 3:2:
$\frac{5x - 75}{\frac{y}{2}} = \frac{3}{2}$
This simplifies to:
$2(5x - 75) = 3y$, or $10x - 150 = 3y$ (Equation 2).
We now solve the system of two equations: 1. $7x + y = 187$ and 2. $10x - 150 = 3y$.
From Equation 1, we can express $y$ as:
$y = 187 - 7x$.
Substitute this expression for $y$ into Equation 2:
$10x - 150 = 3(187 - 7x)$,
$10x - 150 = 561 - 21x$,
$31x = 711$,
$x = 23$.
Now, substitute $x = 23$ back into Equation 1 to find $y$:
$7(23) + y = 187$,
$161 + y = 187$,
$y = 26$.
The number of unsold fruits are: Apples: $5(23) - 75 = 115 - 75 = 40$.
Mangoes: $2(23) - 26 = 46 - 26 = 20$.
Oranges: $\frac{26}{2} = 13$.
The total number of unsold fruits is:
$40 + 20 + 13 = 66$.