half life of a radioactive substance is 3.20h. what is the time taken for 75% of the substance to be used.
Answers
Answer:
Given
a
2
=13 and a
5
=25
We know that
a
n
=a+(n−1)d
∴a
2
=a+(2−1)d
⇒13=a+(2−1)d
⇒a+d=13 ...(i)
and a
5
=a+(5−1)d
⇒25=a+4d
⇒a+4d=25 ...(ii)
Now, subtracting (i) from (ii), we get
3d=12
⇒d=4
Now a+d=13 [from (i)]
⇒a=9
Hence, a
7
=a+6d=9+6(4)
⇒a
7
=33This is a classic example of finding mean and standard deviation using Z values.
From this page find the Z value corresponding to 31% area under the curve and 92% (100-8) percent area under the curve.
Math Is Fun Virtual Manipulative
Note: You'll probably be given tables to lookup in your quizzes.. they're a bit confusing. But you might as well learn how to use it.
As you know:Important Properties of Set Complements Two relationships in the next theorem are known as De Morgan's Laws for sets and are closely related to De Morgan's Laws for statements. x∈(A∪B)c if and only if x∉A∪B. x∉A∪B if and only if x∉A and x∉B. ... x∉A and x∉B if and only if x∈Ac and x∈Bc.Important Properties of Set Complements Two relationships in the next theorem are known as De Morgan's Laws for sets and are closely related to De Morgan's Laws for statements. x∈(A∪B)c if and only if x∉A∪B. x∉A∪B if and only if x∉A and x∉B. ... x∉A and x∉B if and only if x∈Ac and x∈Bc.
Z=X−μσZ=X−μσ
Put in X and Z values values twice, you'll have two linear equations. Solve them and the answer is yours!