Question 1
When Austin was born, Hina was 3 years old. The sum of their present ages is 39. Find Austin's age when Austin was half of Hina's age (this will happen 15 years ago).
Let Austin's current age = 18, Hina's current age = 21
Given: When Austin was born (0 years old), Hina was 3 years old.
Therefore, Hina is always 3 years older than Austin.
So 21 = 18 + 3 ✓
Condition: Find t such that Austin's age = ½ of Hina's age
Equation: 18 + t = ½(21 + t)
Multiply both sides by 2: 218 + 2t = 21 + t
Simplify: 218 + 2t - t = 21
218 + t = 21
t = 21 - 218
t = 21 - 36 = -15
At that time, Austin's age = 18 + -15 = 3
Verification: When Austin is 3, Hina is 6 = 6
Check: Is 3 = ½ × 6? ½ × 6 = 3.0 ✓
Note: Mathematically, this always equals the age difference (3) because:
event_age = current_a + t = current_a + (current_b - 2·current_a) = current_b - current_a = age_diff
Given: When Austin was born (0 years old), Hina was 3 years old.
Therefore, Hina is always 3 years older than Austin.
So 21 = 18 + 3 ✓
Condition: Find t such that Austin's age = ½ of Hina's age
Equation: 18 + t = ½(21 + t)
Multiply both sides by 2: 218 + 2t = 21 + t
Simplify: 218 + 2t - t = 21
218 + t = 21
t = 21 - 218
t = 21 - 36 = -15
At that time, Austin's age = 18 + -15 = 3
Verification: When Austin is 3, Hina is 6 = 6
Check: Is 3 = ½ × 6? ½ × 6 = 3.0 ✓
Note: Mathematically, this always equals the age difference (3) because:
event_age = current_a + t = current_a + (current_b - 2·current_a) = current_b - current_a = age_diff