Aptitude - Simple Interest - Discussion

Since principal with the interest is given for two consecutive years therefore its easy to get the S.I. Without any formula. You can also subtract from 854 given that you multiply 39 with 4 (years).

What is the percentage of the interest?

You can use the formula, SI= PRT.

Here, R= (854-815)/815= 0.0475, T= 3 years, & P= 815.
Therefore, SI= 815*0.0475*3= 117.
Final answer= 815-117= 698.

You can replace T= 4 years & P= 854, the answer is same.

Amount(A) = Principle(p) + Simple Interest(SI).

The sum of money i.e Principle(p) invested or borrowed results an Amount of 815 in 3 years and 854 in 4 years. Since Rate of interest(R) is not mentioned assume it as same for both.

A1 = P + SI1
815 = P + SI1
P = 815 - SI1--- eq1

A2 = P + SI2
854 = P + SI2
P = 854 - SI2 ----- eq2

eq1= eq2
therefore -----> SI2 - SI1 = 854 - 815 =39
Now,
SI1 = P*T1*R/100 =P*3*R/100
SI2 = P*T2*R/100 = P*4*R/100
SI2 - SI1 = P*R/100

39 = P*R/100 -------> Here we can say T=1year, so this is SI for 1 year
now calculate SI for 3 or 4 years
SI for 1 year = 39
SI for 3 years = 39*3 = 117 Which is SI1 or SI for 4 years = 39*4 = 156 which is SI2.

A1 = P + 117
815 = P + 117
P = 815 - 117 = 698


A2 = P + 156
854 = P+156
P = 854 -156 = 698

So sum of money i.e Principle P = 698.

Let p=x nd after 3year A1=815 nd4year A2=854... A( is total amount)=p+i we no P=(A*100)/(100+TR) .......p nd R is equal for both A1 nd A2 .
so P1 =p2-------(eq1) we have formula P1=(A1*100)/(100+T1R)--------(2)
And P2=(A2*100)/(100+T2R)---------(3)
put eq2 and eq3 on eq 1 and putting all value we go Rate (R)=5.58 value of R input on eq 2 or eq 3 we got the value of p.

Can't this question be solved using formula
p=100*si/r*t.

Total amt = p+si.
815 = p+si.
si = 815-p.
854 = p+si.
si = 854-p.
Substituting in formula,
p = 100*815-si/r*3.

Can anyone please help how to solve using this method of substitution.

Basic formula of to find r% and p%.

When give two amounts and two years to find p formula,
(A1*T2-A2*T1)/T2-T1.

R% FORMULA.
(A2-A1)/(A1*T2-A2*T1).

Thanks for explaining.

@Divya.

Its a initial amount.

Why should we apply like this;

s.i for 1 year = Rs 854-815=39
1yr = 39 then 4y = 156
then 854-156=698.