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3 years ago

If you can solve 20 multiplication facts in one minute how long will it take to solve 50 facts

Mathematics

2 answers:

Ad libitum [116K]3 years ago

8 0

If you can solve 20 multiplication facts in one minute then you could solve 50 multiplication facts in 3 minutes

1 minute = 20 facts

2 minutes = 40 facts

3 minutes = 60 facts

We can check our work by doing the unit rate:

60 facts ÷ 3

____________ <--- fraction bar

3 minutes ÷ 3

= 20 facts

__________ (20 facts per minute)

1 minute

mezya [45]3 years ago

5 0

Answer:

150s or 2 min and 30 s

Step-by-step explanation:

20 facts = 1 min

10 facts = 30s

50 facts = ? min

50 / 10 = 5

30 * 5 = 150s

150s = 2 min and 30 s

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Jlenok [28]

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3 years ago

2.The number of grams A of a certain radioactive substance present at time, in yearsfrom the present, t is given by the formulaA

professor190 [17]

Answer:

Given that,

The number of grams A of a certain radioactive substance present at time, in years

from the present, t is given by the formula

$A=45e^{-0.0045(t)}$

a) To find the initial amount of this substance

At t=0, we get

$A=45e^{-0.0045(0)}$ $A=45e^0$

We know that e^0=1 ( anything to the power zero is 1)

we get,

$A=45$

The initial amount of the substance is 45 grams

b)To find thehalf-life of this substance

To find t when the substance becames half the amount.

A=45/2

Substitute this we get,

$\frac{45}{2}=45e^{-0.0045(t)}$

$\frac{1}{2}=e^{-0.0045(t)}$

Taking natural logarithm on both sides we get,

$\ln (\frac{1}{2})=-0.0045(t)^{}$ $(-1)\ln (\frac{1}{2})=0.0045(t)$ $\ln (\frac{1}{2})^{-1}=0.0045(t)$ $\ln (2)=0.0045(t)$ $0.6931=0.0045(t)$ $t=\frac{0.6931}{0.0045}$ $t=154.02$

Half-life of this substance is 154.02

c) To find the amount of substance will be present around in 2500 years

Put t=2500

we get,

$A=45e^{-0.0045(2500)}$ $A=45e^{-11.25}$ $A=45\times0.000013=0.000585$ $A=0.000585$

The amount of substance will be present around in 2500 years is 0.000585 grams

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1 year ago

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3 years ago

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Sunny_sXe [5.5K]

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