MATH
posted by THOMAS HARDY .
What value of p are
2p1,7 and 3P three consecutive terms of ARITHMETIC PROGRESSION

What value of p are 2p1, 7 and 3p three consecutive terms of an ARITHMETIC PROGRESSION?
Letting a = the common difference, we can write
1(7  a) = 2P  1 and
2(7 + a = 3p
Adding yields 14 = 5p  1 from which p = 3 making the 3 terms 5, 7 and 9. 
figer math for 2nd grade