Question

at what rate percent per annum will $400 yield an interest of $78 in 1 and half year

Answer 1

given,
principal = $400
SI = $78
Time = 3/2
rate = SI × 100/ P × T
=> 70×100/400×3/2
=> 7000/1200/2
=> 7000/600
=> 70/6
=> 11.67%
hence the required rate is 11.67% .

Answer 2

Answer:

Required rate of interest 1 \frac{1}{36} \%

Step-by-step explanation:

Given total money is $400, Interest is $78 and time is 1 and half year= 18 months

We know,

$s.i = \frac{prt}{100}$

Where $p =$Principle

$r =$Rate of interest

$t =$time

We can say

$r = \frac{si \times 100}{pt}$

Now S.I = $\frac{400 \times 18 \times r}{100}$

According to question,

$\frac{400 \times 18 \times r}{100} = 78$

$400 \times 18 \times r = 100 \times 78$

$r = \frac{78 \times 100}{400 \times 18} = \frac{37}{4 \times 9} = \frac{37}{36} = 1 \frac{1}{36}$

Required rate of interest is $1 \frac{1}{36} \%$