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Question

# All rates of interest given here are annual rates. Calculate the rate of interest per year which will earn the given amount of interest: a) Principal $400 time 4 years interest$112, b) Principal $800 time 7 years interest$224

Solution

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Step 1
1 of 2

$SI = \dfrac{Ptr}{100}$

Where $SI$ is the simple interest, $P$ is the principle, $t$ is the time in years, and $r$ is the rate percent.

$\textbf{a)}$

$112 = \dfrac{400 \times 4 \times r}{100}$

Using cross product property:

$r = \dfrac{112 \times 100}{400 \times 4} = \boxed{\color{#c34632}{7 \%}}$

$\textbf{b)}$

$224 = \dfrac{800 \times 7 \times r}{100}$

Using cross product property:

$r = \dfrac{224 \times 100}{800 \times 7} = \boxed{\color{#c34632}{4 \%}}$

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