Answer:
<em>Cathy was born in 1980 and she was 18 years old in 1998</em>
Step-by-step explanation:
<u>Equations</u>
This is a special type of equations where all the unknowns must be integers and limited to a range [0,9] because they are the digits of a number.
Let's say Cathy was born in the year x formed by the ordered digits abcd. A number expressed by its digits can be calculated as

In 1998, Cathy's age was

And it must be equal to the sum of the four digits

Rearranging

We are sure a=1, b=9 because Cathy's age is limited to having been born in the same century and millennium. Thus

Operating

If now we try some values for c we notice there is only one possible valid combination, since c and d must be integers in the range [0,9]
c=8, d=0
Thus, Cathy was born in 1980 and she was 18 years old in 1998. Note that 1+9+8+0=18
Answer:
First Question: <u>63 coins are not nickels.</u>
Second Question: <u>63+n=91</u>
Step-by-step explanation:
For your first question: 29+21=50 and 50+13=63. 63 coins are not nickels.
For your second question: You can do 29+21+13+n=91, I just simplified and said 63+n=91. You can choose.
Hope that this helps! Good luck with what you're working on!
Answer:
f(x) = x(x-1)
Step-by-step explanation:
The easy way to do this is to look at it graphically. an inverse function is reflected across the line y=x. f(x)=x(x-1) is an upward opening parabola when reflected, there are two y-values for all positive values of x. A function can only have one y for every x.
There's no question there. You didn't attach the pic