P dollars equals to an interest rate r for T years= T=P+Prt. An investment of $10,000 grew to at least $12,000 in two years, what is the minimum interest rate at which can be invested ?

Question

I'm not sure how to set this problem. I thought at first I would substitute the years and the dollars into the equation in place of T as 2 and the Dollars P as 10,000, but i do not know if that's how i am supposed to start it

Answer 1

You had the formula right, but in this case, you want an inequality, rather than an equation:

10000 + 10000 * r * 2 >= 12000

10000 * r * 2 >= 2000
r >= 0.1

so, you'd need at least 10% interest for the principal to grow from 10K to 12K in two years