Coin Inequalities
1. **State the problem:** Mayerlin has $x$ dimes and $y$ nickels.
She has no more than 20 coins combined:
$$x + y \leq 20$$
The total value is no less than 1.30 dollars. Since dimes are 10 cents and nickels are 5 cents:
$$0.10x + 0.05y \geq 1.30$$
2. **Rewrite inequalities for graphing:**
Coin count inequality:
$$x + y \leq 20$$
Value inequality multiply by 20 to clear decimals:
$$2x + y \geq 26$$
Or equivalently:
$$y \geq 26 - 2x$$
3. **Explain graph:**
- The region satisfying $x + y \leq 20$ is the area below or on the line $y = 20 - x$.
- The region satisfying $y \geq 26 - 2x$ is the area above or on the line $y = 26 - 2x$.
4. **Find intersection points of two lines:**
Set $20 - x = 26 - 2x$
$$20 - x = 26 - 2x$$
Add $2x$ to both sides:
$$20 + x = 26$$
Subtract 20:
$$x = 6$$
Find $y$:
$$y = 20 - x = 20 - 6 = 14$$
So, intersection is at $(6, 14)$.
5. **Determine possible solution:**
Because $x$ and $y$ represent counts of coins, they must be integers and non-negative.
Try $x=7$, then $y$ should satisfy:
$$x + y \leq 20 \Rightarrow 7 + y \leq 20 \Rightarrow y \leq 13$$
And also
$$y \geq 26 - 2(7) = 26 - 14 = 12$$
Therefore, $12 \leq y \leq 13$.
Choosing $y=12$:
- Total coins: $7 + 12 = 19 \leq 20$ (okay)
- Value: $0.10 \times 7 + 0.05 \times 12 = 0.70 + 0.60 = 1.30 \geq 1.30$ (okay)
Thus $(7, 12)$ is one possible solution.
**Final answer:** One possible integer solution is $x=7$ dimes and $y=12$ nickels.