An element with a mass of 840 grams decays by 7% per minute. To the nearest minute, how long will it be until there are 200 grams of the element remaining?

The element takes 19.78 minutes to reach 200 grams, if an element with a mass of 840 grams decays by 7% per minute.

Step-by-step explanation:

The given is,

                  Mass of an element.

                  Decays by 7% per minute.

Step: 1

                 Formula to calculate the mass of element with an decay rate after some time period,

                                ..........................(1)

                 Where, F - Mass of element after t period

                              P - Mass of element at initial

                               r - Rate of decay of element

                               t - Time in minutes

Step: 2

                 From the give values,

                            F = 200 grams

                            P = 840 grams

                             r = 7 % per minute

                Equation (1) become,

               Take log on both sides,

                 ㏒ 0.238095 = (t) ㏒ 0.93

                   -0.6232493 = (t) (-0.03151705)

                                        =  19.77498

                                     t ≅ 19.78 minutes

Result:

              The element takes 19.78 minutes to reach 200 grams, if an element with a mass of 840 grams decays by 7% per minute.

here is the

mark brainliest pl

hello,

b) 62.47% of the students are between 14 and 18 years old.

step-by-step explanation:

mean = 15 and standard deviation = 2

student between 14 to 18

formula used z-score

for age 14 , z score

using z-table , p(z> -0.5)=0.3085

for age 18 , z score

using z-table , p(z< 1.5)=0.9332

p(-0.5< z< 1.5)=0.9332-0.3085 = 0.6247

thus, 62.47% of the students are between 14 and 18 years old.

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