ans: Robi is 40 years and his son is 16 years.
Let, Age of Robi be = x
Age “Robi’s son be = y
For the question
(x – 8) = 4 (y – 8)
=> x – 8 = 4y – 32
=> x – 4y = – 32 + 8
=> x – 4y = – 24 —————— (i)
=> x + 8 = 2y + 16
=> x – 2y = 8 ————-~-—— (ii)
Now (i) — (ii)
=> 2y = – 32
y= 16
Putting the value of y in eqn (i)
x-4 x16 =-24
=> x = -24 +64
x=40
ans: 400.
Only passed in English = 80 – 75 = 5%
Only passed in Mathematics = 85 – 75 = 10%
Passed in both subjects = 5 + 10 + 75 = 90%
Failed in both subjects = 100 – 90 = 10%
Failed students 10 when total students = 100
Failed students 40 when total students = $\frac{100\times 40}{10}$ = 400.
ans: A invested 2,70,000, B invested 1,80,000 & 3,60,000.
Let, A invested initially = 3x
B invested initially = 2x
C invested initially = 4x
From the question,
$\frac{3x\times 36}{2x\times 36+24\times 270000}$ = $\frac{3}{4}$
=> $\frac{108x}{72x+6480000}$ = $\frac{3}{4}$
=> 432x – 216x = 6480000 x 3
x = 90,000
A invested = 3 x 90,000 = 2,70,000
B invested = 2 x 90,000 = 1,80,000
C invested = 4 x 90,000 = 3,60,000
