At what rate percent per annum will the simple interest on a sum of money be 2/5 of the amount in 10 years

Answer: Option D

Explanation:

Let sum = x
Time = 10 years.
S.I = 2x /5, [as per question]
Rate =( (100 * 2x) / (x*5*10))%
=> Rate = 4%

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 D

Explanation:

Here firstly we need to calculate the principal amount, then we can calculate the new rate.

$$\begin{aligned} P = \frac{S.I. * 100}{R*T} \\ P = \frac{840 * 100}{5*8} \\ P = 2100 \\ \text{Required Rate = } \frac{840 * 100}{5*2100} \\ R = 8\%\\ \end{aligned}$$

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 D

Explanation:

We need to calculate the total amount to be paid by him after 4 years, So it will be Principal + simple interest.

So,
$$\begin{aligned} => 500 + \frac{500*5*4}{100} => Rs. 600 \end{aligned}$$