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I am Lyosha [343]
3 years ago
8

The half-life of lead is 22 years. How long will it take for a sample of this substance t decay to 80% of its original amount?

Mathematics
1 answer:
Svetlanka [38]3 years ago
4 0

Answer: 7 years

Step-by-step explanation:

t_{\frac{1}{2} } = In2 / ∧

since the half life is given , we have :

22 = In 2/ ∧

∧ = In2/22

∧ = 0.032

Recall the formula for half life:

\frac{N(t)}{N(0)} = e^{-∧t}

Therefore:

0.80 = e^{-0.032t}

Take the In of both sides

In 0.80 = - 0.032t

t = In 0.80 / - 0.032

t = 7 years

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Question:
DanielleElmas [232]

Given A room is half as long again as it is broad

Let the breadth of the room x m

length of the room x + x/2 = 3x/2m

Area of the room , x × 3x/2 =<em> 3x²/2m</em>

Given , cost of carpeting the room at Rs. 3.25m⁻²

So , total cost , 3x²/2 × 3.25

But , Total cost of carpeting is given as 175.50 so ,

  • (3x²/2 )× 3.25 = 175.50
  • x² = 175.50 × 2 / 3.25 × 3
  • x² = 36
  • x = 6

  • Breadth x = 6 m
  • length 3x/2 = 9m

let the height of the room H m

Area of the four wall = 2(L+ b)× h 2(6+9)× H

= 30H m²

Area of the of the one door and two window is 8m²

8m² Area to be prepared = Area of four wall - area of two window and 1 door = (30H - 8) m²

Given cost of preparing wall is Rs. 1.40m²

total cost of preparing wall is (30H - 8) × 1.40

Total cost of preparing wall is given as 240.80

comparing , (30H - 8 ) × 1.40 = 240.80

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Hence, Dimensions of the room are lengths 9m , breadth 6m and height 6m

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