Translating a mixed-fraction condition: The sum of one-half and one-fifth of a number exceeds one-third of that number by 7 1/3. What is the number?

Difficulty: Easy

Correct Answer: 20

Explanation:


Introduction / Context:
Convert words into an algebraic equation involving fractions, then solve for the unknown number. Mixed fractions should be converted to improper fractions to simplify arithmetic.

Given Data / Assumptions:

  • (1/2 + 1/5)x − (1/3)x = 7 1/3.
  • 7 1/3 = 22/3.


Concept / Approach:
Combine like terms on the left: (1/2 + 1/5 − 1/3)x. Compute the common denominator and simplify to get a single coefficient times x. Then isolate x.


Step-by-Step Solution:

1/2 + 1/5 = 7/10.7/10 − 1/3 = 21/30 − 10/30 = 11/30.(11/30)x = 22/3 ⇒ x = (22/3) * (30/11) = (22*30)/(33) = 660/33 = 20.


Verification / Alternative check:
Check: (1/2 + 1/5) of 20 = (10 + 4) = 14; one-third of 20 = 20/3 ≈ 6.666…; difference 14 − 6.666… = 7.333… = 7 1/3, correct.


Why Other Options Are Wrong:

  • 15, 18, 30: Do not satisfy the exact fractional relation; plugging them in fails the difference test.


Common Pitfalls:
Misconverting 7 1/3 to an improper fraction or adding fractions without a common denominator.


Final Answer:

20

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