Consider the suggested option:
1) if in 20 gr. of 50% solution given, then pure salt in this mix is 0.5*20=10 gr., and pure water is 0.5*20=10 gr.
2) after Maya added 5 gr. pure salt is 10+5=15 gr. Total mass of mix is 15(pure salt)+10(pure water)=25 gr.
3) new solution is 15/25=0.6 or 60%.
Answer: 25 gr. of 60% salt solution.

7 0

3 years ago

Use the initial term and the recursive formula to find an explicit formula for the sequence an. Write your answer in simplest fo

agasfer [191]

From the recursive rule

$a_n = a_{n-1}-13$

it follows that

$a_{n-1}=a_{n-2}-13 \implies a_n = a_{n-2} - 2\times13$

$a_{n-2}=a_{n-3}-13 \implies a_n = a_{n-3} - 3\times13$

and so on. Notice how the subscript on a on the right side and the coefficient multiplied by 13 add up to n (n - 2 + 2 = n; n - 3 + 3 = n; and so on). If we continue the pattern, we'll end up with

$a_n = a_1 + (n-1)\times13$

so that the explicit rule for the n-th term in the sequence is

$a_n = -2 + 13(n-1) \implies a_n = \boxed{13n-15}$

6 0

2 years ago