# Large percentage problem: check my work please?

1. Apr 28, 2007

### Holocene

The universe is thought to be 13.7 Billions years old. If you lived to be 100, what percentage of the total age of the universe would coincide with your lifetime?

I get .0000007% or seven 10-Millionths of one percent.

Is this correct?

2. Apr 29, 2007

### Gib Z

$$\frac{100}{1.37\cdot10^{10}} \cdot 100 = \frac{10^4}{1.37\cdot 10^{10}} = \frac{1}{1.37\cdot10^6} = 7.2992700729927\cdot 10^{-8}$$

So you got close, but theres a bit more accurate.

3. Apr 29, 2007

### Holocene

I'm a bit confused here.

1 / 1.37 x 10^6 = 1 / 1,370,000 = 0.00000073 = 7.3 x 10^-7

7.3 x 10^-7 does not equal 7.2992700729927 x 10^-8

What am I doing wrong???

4. Apr 29, 2007

### Gib Z

Well first when you have 13.7 BILLION years the exponent of the 10 is 9, not 6. 6 Is for million. So its 13.7 x 10^9. 13.7 is 1.37 x 10, so it becomes 1.37x10^10

I don't see what the problem should be, you have the right answer in the beginning! I just gave it a bit more accurately.

5. Apr 29, 2007

### Moo Of Doom

You did the right steps, just made a typo at the end.

$$\frac{1}{1.37\cdot10^6} = 7.2992700729927\cdot 10^{-7}$$
not
$$\frac{1}{1.37\cdot10^6} = 7.2992700729927\cdot 10^{-8}$$

6. Apr 30, 2007

### Gib Z

Damn it! Yes Moo's right...

7. May 1, 2007

### uart

I find this thread really ironic. Holocene got the most correct answer, though apparently by accident of inexperience with his calculator and scientific notation etc.

Gib Z and Moo, you should know it's bad form to give an answers to 15+ significant digits when the data on which the calculations are based is dubious at even two or three significant digits.

Last edited: May 1, 2007
8. May 2, 2007

### Gib Z

14 hehe..Lets settle with $7.3 \cdot 10^{-7}$ :)