If you divide two hundred and thirty-six by four, you have fifty-nine groups; each consisting of three boys and one girl. If you multiply fifty-nine by three, you are presented with the number of boys- one hundred and seventy seven. (:

4 0

3 years ago

The half-life of cesium-137 is 30 years. Suppose we have a 20 mg sample.

Tju [1.3M]

Answer:

(a) A = (20mg)/(2^(t/30))

(b) 12.6mg

Step-by-step explanation:

To calculate the amount remaining after a number of half-lives, n, we can make use of:

$A = \frac{B}{2^n}$

Where A = amount remaining

B = initial amount

$n = \frac{t}{t_{0.5}}$

(a) A = (20mg)/(2^(t/30))

(b) Mass after 20years

A = (20mg)/(2^(20/30)) ≈ 12.6mg

1mg = (20mg)/(2^(t/30))

$20mg = {2^{\frac{t}{30}}$

Taking log of both sides we have:

Log(20) = (t/30)log(2)

t/30 = (log(20))/(log(2)) ≈ 4.3

t/30 = 4.3

t = 30 x 4.3 ≈ 129.6years.

8 0

3 years ago

It took Amir 2 hours to hike 5 miles. On the first part of the hike, Amir averaged 3 miles per hour. For the second part of the

Natasha_Volkova [10]

We can say that x is the amount of time of the first (easier) part of the hike. Ans t is the amount of time of the second ( more difficult ) part of the hike.
x = 2 - t
And:
3 x + 1.5 t = 5
Answer:
The equation is:
3 * ( 2 - t ) + 1.5 t = 5
We can also solve this equation:
6 - 3 t + 1.5 t = 5
1.5 t = 1
t = 0.66 h = 2/3 h = 40 min.

5 0

3 years ago

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