The left and right page numbers of an open book are two consecutive intergers whose sum is 199 find these page numbers

Let's make an equation.
x+y=199
Let's have x be the larger number. Since they are consecutive, they are one away. Let's make an equation for x.
y+1=x; Let's plug this into the first equation.
(y+1)+y=199
2y+1=199; subtract one.
2y=198
Divide.
198÷2=99
So, the smaller number is 99, so the bigger number is 100. You could also tell that 199 can be split into 100 and 99, which are consecutive numbers.