a) 8%

b) 10%

c) 12%

d) 12 ½%

correct answer is: b) 10%

**Explanation**

Here ‘a sum’ means ‘principal’.

Let,

Principal = ₹'x'

Rate = r %

Time = 10 years.

So, according the question,

Simple Interest =\frac{p\times t\times r}{100}

\rightarrow\ 2x=\frac{x\times10\times r}{100} _{[put the value]}

\rightarrow\ x\times10\times r=2x\times100 _{[cross multiply]}

\rightarrow\ 10xr=200x

\rightarrow r=\frac{200x}{10x}

\rightarrow\ r = 10

\therefore Rate percent per annum will 10 %**Ans:** Rate percent per annum will 10 %.

**Another way to phrase this particular query is:****1. What is the annual simple interest rate needed for a sum to double in 10 years?****2. Calculate the percentage rate per annum for simple interest to double a sum in 10 years.****3. At what interest rate per annum will a principal amount double in 10 years with simple interest?****4. Determine the simple interest rate required for a sum to become double within a span of 10 years.****5. Find the annual percentage rate for simple interest that results in a sum doubling in 10 years.**