Multiple choice

The average age of three girls is $35$ years. The ratio of their age is 3:5:7. Find the age of the youngest one

  1. $12$
  2. $17$
  3. $21$
  4. $23$
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C Correct answer
Explanation

Sum of ages = 35 * 3 = 105. Ratio 3:5:7 means 3x + 5x + 7x = 15x = 105, so x = 7. Youngest age = 3x = 3 * 7 = 21.

AI explanation

Let the ages of the three girls be 3x, 5x, and 7x based on the given ratio. The sum of their ages is 15x, and using the basic average formula, this sum equals 3 times the average of 35 years, which is 105 years. Solving the equation 15x = 105 gives x = 7. The youngest girl corresponds to the ratio value 3x, so her age is 3 times 7, which is 21 years.

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