Alexandra invests some money into an account that pays 0.5% compound interest per annum. Work out after how many years Alexandra will have doubled the investment.

200 Years

Step-by-step explanation:

0.5% X 10 = 5% Increase. So after 10 years 5% Increase

0.5% X 100 = 50% increase. So after 100 years 50% Increase

0.5 X 200 = 100% Increase. So after 200 years it will double.

c.

step-by-step explanation:

she should of added 9^2 and 12^2. that is because it is a^2+b^2=c^2. c^2 is the hypotenuse and should always be bigger than the other two numbers. which is why she should of added 9 squared and 12 squared together instead of 15 squared.