Question

Math help questions ​

Answer 1

Answer:

25 years

Step-by-step explanation:

total = before × percent ( in decimal ) × time

1400 = 800 × 0.07 × t

1400 = 56 × t

1400 ÷ 56 = 25

t = 25

Hope this was helpful!

Answer 2

After 1 year, the initial investment increases by 7%, i.e. multiplied by 1.07. So after 1 year the investment has a value of $800 × 1.07 = $856.

After another year, that amount increases again by 7% to $856 × 1.07 = $915.92.

And so on. After t years, the investment would have a value of $\ 800 \times 1.07^t$.

We want the find the number of years n such that

$\ 856 \times 1.07^n = \ 1400$

Solve for n :

$856 \times 1.07 ^n = 1400$

$1.07^n = \dfrac74$

$\log_{1.07}\left(1.07^n\right) = \log_{1.07}\left(\dfrac74\right)$

$n \log_{1.07}(1.07) = \log_{1.07} \left(\dfrac74\right)$

$n = \log_{1.07} \left(\dfrac74\right) = \dfrac{\ln\left(\frac74\right)}{\ln(1.04)} \approx \boxed{8.3}$