Respuesta :
Given:
Four years ago average age of A , B & C was 25 years.
Find:
A's present age
Solution:
Let the ages of A , B , C be A , B , C years.
- Age of A before 4 years = (A - 4) years.
- Age of B before 4 years = (B - 4) years.
- Age of C before 4 years = (C - 4) years.
We know that,
Average = Sum of observations/Number of observations.
Here,
Sum of observations = A - 4 + B - 4 + C - 4 = (A + B + C - 12) years.
Number of observations = 3.
So, (A + B + C - 12)/3 = 25
⟹ A + B + C - 12 = 3 * 25
⟹ A + B + C = 75 + 12
⟹ A + B + C = 87 -- equation (1)
Also given that,
Average age of B & C before 5 years was 20 years.
⟹ (B - 5 + C - 5)/2 = 20
⟹ B + C - 10 = 2 * 20
⟹ B + C = 40 + 10
⟹ B + C = 50 -- equation (2)
Subtract equation (2) from equation (1).
⟹ A + B + C - (B + C) = 87 - 50
⟹ A + B + C - B - C = 37
⟹ A = 37 years
∴ A's present age is 37 years.
I hope it will help you.
Regards.
Answer:
→ md - 2nd + 3md = 2 * [ a + (n - 1)d ]
→ 4md - 2nd = 2 * [ a + (n - 1)d ]
→ 2(2md - nd) = 2 * (a + nd - d)
→ 2md - nd - a + d = nd
→ 2md - nd - (md - 2nd) + d = nd
[ From equation (1) ]
→ 2md - nd - md + 2nd + d = nd
→ md + nd + d = nd
→ (m + n + 1)d = n * d
→ (m + n + 1) = n
Step-by-step explanation:
