A textbook store sold a combined total of 228 biology and physics textbooks in a week. The number of blology textbooks sold was three times the number of physics textbooks sold. How many textbooks of each type were sold?

Step-by-step explanation:

Let us assume p is the number of psychology books and b is the number of biology textbooks.

set up first equation:

we know that the total number of books sold was 393

p+b=393

set up second equation:

we know that there were 79 less biology book sold that psychology so...

p = b + 79

subsitute p in the first equation to solve for b

solve value for p

step-by-step explanation: a reaction is first order. if the initial reactant concentration is 0.0200 m, and 25.0 days later the concentration is 6.25 x 10-4 m, then its half-life is:

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