Answer: 64.29%
Step-by-step explanation:
Let the total earnings of the Lee family in May be x
Amount earned by Mr Lee in May = 60% of x = 0.6x
Amount earned by other family members in May = x - 0.6x (total earnings - Mr Lee's earnings) = 0.4x
Amount earned by Mr Lee in June = 20% more than what Mr Lee earned in May.
That is, amount earned by Mr Lee in June = 1.2 × 0.6x = 0.72x
Amount earned by other members of the family in June remains unchanged, that is = 0.4x
Total amount earned by the Lee family in June = 0.72x + 0.4x = 1.12x
Percentage of total earnings in June earned by Mr. Lee = (0.72x/1.12x) × 100% = 64.29%.
QED!