AlgebraMediumStamps of two values
Algebra practice question
Lena buys 24 stamps. Some cost 20 cents each and the rest cost 50 cents each, and she pays $7.80 in total. How many 50-cent stamps does she buy?
Answer: 10
With f fifty-cent stamps: 20(24 − f) + 50f = 780 gives 30f = 300, so f = 10.
Common wrong answers
- If you answered 12
- 12 assumes an even split.
- If you answered 14
- 14 is the number of 20-cent stamps.
- If you answered 15.6
- 15.6 divides 780 by 50, ignoring the cheaper stamps.
More Algebra questions
- Medium
A system: 2x + y = 11 and x − y = 1. What is the value of x + y? - Medium
Which of the following describes all solutions to 4x − 9 ≤ 2x + 5? - Medium
A phone's battery percentage is modeled by P = 100 − 8t, where t is the number of hours since it was unplugged… - Medium
If y = 2x − 1 and 3x + y = 14, what is the value of x? - Medium
If |2x − 3| = 7, what is the sum of all possible values of x? - Medium
Line k has equation y = (2/3)x + 1. Which equation represents a line perpendicular to line k?
Not affiliated with the College Board. SAT is a trademark of the College Board.