Find the rate at Simple interest, at which a sum becomes four times of itself in 15 years.

Answer: Option C

Explanation:

$$\begin{aligned} \text{ S.I. = } \frac{P \times R \times T}{100} \end{aligned}$$
So, by putting the values in the above formula, our result will be.
$$\begin{aligned} \text{ Required result = } \frac{7000 \times 50 \times 9}{3 \times 12 \times 100} = 875 \end{aligned}$$

[Please note that we have divided by 12 as we converted 9 months in a year format]

Answer: Option A

Explanation:

Let the sum is 100.

As financier includes interest every six months., then we will calculate SI for 6 months, then again for six months as below:

SI for first Six Months = (100*10*1)/(100*2) = Rs. 5

Important: now sum will become 100+5 = 105

SI for last Six Months = (105*10*1)/(100*2) = Rs. 5.25

So amount at the end of year will be (100+5+5.25)
= 110.25

Effective rate = 110.25 - 100 = 10.25

Answer: Option C

Explanation:

Two things need to give attention in this question, First we need to calculate gain for 1 year only.
Second, where we take money at some interest and lends at other, then we use to subtract each other to get result in this type of question. Lets solve this Simple Interest question now.

$$\begin{aligned} \text{Gain in 2 year = } \\ [(5000 \times \frac{25}{4} \times \frac{2}{100})-(\frac{5000 \times 4 \times 2}{100})] \\ = (625 - 400) = 225 \\ \text{ So gain for 1 year = }\\ \frac{225}{2} = 112.50 \end{aligned}$$

Answer: Option B

Explanation:

Let sum be x and rate be r%
then, (x*r*15)/100 = 3x [important to note here is that simple interest will be 3x not 4x, beause 3x+x = 4x]

=> r = 20%

Answer: Option A

Explanation:

S.I. = 956 - 800 = Rs 156

$$\begin{aligned} R = \frac{156*100}{800*3} \\ R = 6\frac{1}{2}\% \\ \text{ New Rate = }6\frac{1}{2}+4 \\ = \frac{21}{2} \% \\ \text{ New S.I. = }800\times\frac{21}{2}\times{3}{100} \\ = 252 \end{aligned}$$

Now amount will be 800 + 252 = 1052