Question

1. a first train travelling at x km an hour takes t hour less to travel y km than a slower one takes to travel z km . find the different between their speed
2. a man has one kind of coffee at 'a' paise
per kg and another at 'b' paise per kg how much of each must take to form a mixture of (a0b)kg which b can sell at c paise /kg without loss.

Answer 1

I suggest you replace the variables with actual numbers and solve that problem.
Then repeat the same steps using the variables in the given question.

e.g.
A first train travelling at 60 km an hour takes 2 hour less to travel 300 km than a slower one takes to travel 150 km . find the different between their speed

time for 1st train = 300/60
time for 2nd train = 300/60 + 2
speed of 2nd train = 150/(300/60 + 2)

difference in speeds = 60 - 150/(300/60 + 2)
( I purposely left the arithmetic open, so that you can see where the variables go)

in the second question, I have no idea what (a0b)kg means