Explanation:
1.
x = number
x/4 = x/3 - 1
x/3 - x/4 = 1
4x/12 - 3x/12 = 1
x/12 = 1
x = 12
2.
the numerator is the top (it gives the number of the parts of the whole that are combined in the fraction).
the denominator is the bottom (it says in how many and therefore how small parts we split the whole).
x = numerator
y= denominator
fraction is x/y
y = x + 2
(x+3)/(y+3) = 23
x + 3 = 23(y + 3) = 23y + 69
x = 23y + 66
now we use the first equation (y = x + 2) and substitute it into the last equation :
x = 23(x + 2) + 66 = 23x + 46 + 66 = 23x + 112
x = -112/22 = -56/11
y = -68/22 = -34/11
the original fraction is
x/y = -56/11 / -34/11 = -56/11 × -11/34 = 56/34 = 28/17
3.
in 1 hour the large pipe has done 1/3 of the work. and the small pipe 1/6 of the work.
so, in total in 1 hour we get (1/3 + 1/6) done.
what factor do we need to multiply (1/3 + 1/6) to get 1/1 (the whole work) ?
x(1/3 + 1/6) = 1
x(2/6 + 1/6) = 1
x(3/6) = 1
x × 1/2 = 1
x = 2
it takes both pipes together 2 hours to empty the pool.
4.
very similar to 3.
we are just using days instead of hours.
in 1 day Erwin gets 1/2 of the work done and Ana 1/5 of the work. so, together, 1/2 + 1/5 of the total work in one day.
so, how many days to get 1/1 (the whole work) done ?
x(1/2 + 1/5) = 1
x(5/10 + 2/10) = 1
x(7/10) = 1
7x = 10
x = 10/7
it takes them together 10/7 days to mow the whole lawn.