# How do you find the amount of time given I=$54, P=$800, r=4.5%?

Dec 12, 2016

$1 \frac{7}{9}$ years

#### Explanation:

Words used in question indicate that when a principal amount $P$, is invested for a time of $t$ years at a rate of $r$, the interest earned is $I$.

In such cases as I=(P×r×t)/100, we can have t=(I×100)/(P×r).

As we have to calculate time $t$ given I=$64, P=$800 and r=4.5%,

t=(64×100)/(800×4.5)

= (64×cancel100^1)/(cancel800^8×4.5)

= 64/(8×4.5)

= $\frac{64}{36}$ (and dividing by $4$)

= $\frac{16 \cancel{64}}{9 \cancel{36}}$

= $\frac{16}{9} = 1 \frac{7}{9}$ years.