Find the four numbers in A.P., whose sum is 50 and in which the greatest number is 4 times the least.
Given: Sum of four terms is 50
To find: first four terms of AP
Assume these four terms are a - 2d, a - d, a + d, a + 2d
Sum of these terms is 4a = 50
It is also given that the greatest number is 4 time the least
a + 2d = 4(a - 2d)
3a = 10d
Substituting 
Hence the terms of AP are a - d, a, a + d which is 
3