OG详解-OG7 数学2 Q15

Choice C is correct. It’s given that t represents the number of years since the account was opened. Therefore,  t​10​ represents the number of 10-year periods since the account was opened. Since the value of the account doubles during each of these 10-year periods, the value of the account can be found by multiplying the initial value by t​10​ factors of 2. This is equivalent to 2t​10​ . It’s given that the initial value of the account is $890. Therefore, the value of the account  M(t), in dollars, t years after the account was opened can be represented by M(t)=890(2)​t10​  .  
Choice A is incorrect. This equation represents the value of an account if the value of the account halves, not doubles, every 10 years. Choice B is incorrect. This equation represents the value of an account if the value of the account decreases by 90%, not doubles, every 2, not 10, years. Choice D is incorrect. This equation represents the value of an account if the value of the account increases by a factor of 10, not doubles, every 2, not 10, years.