Assuming that the 4.8% interest rate is an annual interest rate, then, after one year, with a principal of $3,000 we would be able to win 4.8% of $3000:
Divide 144 over 12 to find the monthly earnings:
Therefore, with a principal of $3,000 we would be earning $12 interest in 1 month.
For the earnings on the first month to be equal to $10, then you would have to win $120 annually, and $120 must be 4.8% of the principal. To find which quantity satisfies that 4.8% of it is equal to $120, divide 120 over 4.8%:
Therefore, the principal must be equal to $2500 for you to win $10 on the first month, and it would indeed be correct to say that if you open an account with $3000 you will earn at least $10 interest in 1 month.