Gappu invested Rs X at 8% simple interest for three years in a scheme and he invested the same sum for four years at 4% simple interest in another scheme. If the total interest get by Gappu from both the schemes is Rs 398, then find X.

The correct answer is 995.

Let's find the value of X step-by-step using the formula for Simple Interest (SI):

$SI=\frac{P\times R\times T}{100}$

where:
- $P$ is the Principal amount invested,
- $R$ is the Rate of interest per annum, and
- $T$ is the Time period in years.

Step 1: Calculate the interest from the first scheme
Gappu invested Rs $X$ at a rate of 8% for 3 years.
$Interest from scheme 1=\frac{X\times 8\times 3}{100}=\frac{24X}{100}$

Step 2: Calculate the interest from the second scheme
Gappu invested the same sum of Rs $X$ at a rate of 4% for 4 years.
$Interest from scheme 2=\frac{X\times 4\times 4}{100}=\frac{16X}{100}$

Step 3: Set up the equation for total interest
The total interest obtained from both schemes is given as Rs 398.
$\frac{24X}{100}+\frac{16X}{100}=398$

Combine the fractions:
$\frac{40X}{100}=398$

Simplify the fraction:
$0.4X=398$

Solve for $X$:
$X=\frac{398}{0.4}$

$X=995$

Therefore, the value of the invested sum $X$ is Rs 995.