Answer:
45.88 seconds
Step-by-step explanation:
= Time taken to sing the fist time = 
Time taken to sing the second time was
less than the first time so

Time taken to sing the third time was
less than the the second time

So the time it took the choir to sing the third time was 45.88 seconds.
Answer: 18 books
Step-by-step explanation:
In this problem, it will be helpful to know the vertex form of a parabola, which is listed below:

is a constant which helps to determine whether the parabola opens up or down. If
, then the parabola opens downward and if
, the parabola opens upwards
is the vertex of the parabola
By looking at the graph, we can first see that the graph opens downwards, meaning that
. Thus, choices C and D are not valid. Now, let's use the vertex of the parabola to complete the equation.
The vertex of this parabola is (-1, 3), as shown by the graph. When we substitute this into our formula, we get:

The answer is a,
.
Answer:
x + y = 49
y = x - 15
Step-by-step explanation:
The sum of 2 numbers is 49 means that x+y = 49. (The two numbers are x and y, and the sum of them are 49.)
The second number is 15 less than the first number, means that y = x - 15 (The second number is y, and it is 15 less than x, which is the first number.)
Therefore the equations will be
x + y = 49
y = x - 15