Q: Red pens cost twice as much as blue pens. Two blue pens and three red pens cost a total of $2.32. How much does a blue pen cost?
Explanation: Let r be the cost of a red pen, and let b be the cost of a blue pen.
Then, r = 2b and 2b + 3r = 2.32. Solve this system of equations.
r + 3r = 2.32
4r = 2.32
r = 0.58
Plug r= 0.58 into the first equation (or second, but I like the first better):
0.58 = 2b
0.29 = b
You can also use other algebraic methods such as elimination, Cramer’s Rule, etc. Or use my TI-84 Plus program CRAMER once you rearrange the system to say: 2b – r = 0 and 2b + 3r = 2.32.