Simple interest
 A certain sum at simple interest amounts to Rs 1040 in 3 Yr and to Rs 1360 in 7 yr.Then the sum is ?

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Simple Interest for 4 yr = Rs( 1360  1040 ) = Rs 320
So, Simple Interest for 3 yr = Rs [(320/4) x 3]= Rs 240Correct Option: B
Simple Interest for 4 yr = Rs(1360  1040 ) = Rs 320
so, Simple Interest for 3 yr= Rs [(320/4) x 3]= Rs 240
Sum = Rs (1040240)= Rs 800
 At what rate percent per annum simple interest , will a sum of money triple itself in 25 year?

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Rate R = (100 x SI)/(P x T)
where , SI= Simple Interest
T= TimeCorrect Option: A
Let principal amount = P
As amount =3P, T=25 yr
∴ SI=3PP=2P
∴ Rate R = (100 x SI)/(P x T)
where, SI= Simple Interest T = Time
= (100 x 2P)/(P x 25)=8%
 The difference of 13% per annum and 12% of a sum in 1 year is Rs 110.Then the sum is ?

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Let the sum be 'y'
then, [(y x13 x 1)/100][(y x 12 x 1)/100]=110Correct Option: C
Let the sum be 'y'
then, [(y x13 x 1)/100 ] [( y x 12 x 1) / 100]=110
since ( y / 100 ) = Rs 110
∴ Y = Rs 11000
 A sum of money at simple interest amount to Rs 1260 in 2 yr and Rs 1350 in 5 yr, then the rate percent per annum is ?

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Simple in 3 year = Rs( 1350  1260) = Rs 90
Simple in 2 year = (2/3) &time; 90= Rs 60
Rate, R= (100 x SI)/(P x T)
where , SI= Simple Interest
P= Principal
T= TimeCorrect Option: C
Simple in 3 year = Rs( 1350  1260) = Rs 90
Simple in 2 year = (2/3) &time; 90= Rs 60
Principal = Rs (1260 60)= Rs 1200
Rate, R= (100 x SI)/(P x T)= (100 x 60)/(1200 x 2)=60/24= 25 %
where , SI= Simple Interest
P= Principal
T= Time
 If a certain sum is doubled in 8 yr on simple interest, in how many year will it be four times?

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Let the sum be Rs 'y' , so amount = 2y
Simple interest =Rs y
Let R be the rate of interest,
R= (100 x SI)/(P x T)
where SI= Simple Interest
P = Principal
T = TimeCorrect Option: A
Let the sum be Rs 'y' , so amount = 2y
Simple interest =Rs y
Let R be the rate of interest,
R= (100 x SI)/(P x T) = (100 x y) / (y x 8) = 12.5 %
where SI= Simple Interest
P = Principal
T = Time
now, the needed amount = Rs 4y
since SI = Rs (4xx)= Rs 3y
since T= (100 x SI)/(P x R)
= (100 x 3y )/(y x 125)= 24 yr