AlgebraVery hardCoins of two kinds from a count and a total
Algebra practice question
A jar holds only 5-cent coins and 10-cent coins. There are 30 coins with a total value of 2 dollars and 30 cents. How many 10-cent coins are in the jar?
Answer: 16
With f five-cent and t ten-cent coins, f + t = 30 and 5f + 10t = 230. Substituting f = 30 − t gives 150 + 5t = 230, so t = 16.
Common wrong answers
- If you answered 14
- 14 is the number of 5-cent coins.
- If you answered 23
- 23 divides 230 by 10.
- If you answered 46
- 46 divides 230 by 5.
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