Answer:
Step-by-step explanation:
WE are given that 
. Then, to now the first for terms, we must replace n by 1,2,3,4 respectively. Then
Note that as n increase, 
gets closer to 0. So, the limit of this sequence is 0.
a = amount (in oz) of solution A
b = amount of solution B
The scientist wants a mixture of 110 oz, so
a + b = 110
Solution A consists of 65% salt, so each ounce of solution A contributes 0.65 oz of salt; similarly, each ounce of B contributes 0.9 oz. The mixture is supposed to consist of 75% salt, which amounts to 0.75 * (110 oz) = 82.5 oz of salt. So
0.65 a + 0.9 b = 82.5
Solve for a and b:
b = 110 - a
0.65 a + 0.9 (110 - a) = 82.5
0.65 a + 99 - 0.9 a = 82.5
0.25 a = 16.5
a = 66 ==> b = 44
77/5=99/x
77x=5*99
77x=495
x=495/77
x=6.4
she needs to study 6.4 hrs to get 99
-7x-5y=-47x+9y=-4
combine like terms to cross out the 7x
solve for y, to get -2
plug it back in to one of the equations and x is 2
y=-2
x=2
