Community technical college
posted by Benjamin on .
Given that 1st term of an A.P is 7 and it's 10th term is twice the second term,calculate the (a) 19th term (b)sum of 28 terms (c) difference between 9th and 6th terms

Statistics??
What's the SUBJECT?? 
a10=a1+r(101)
14=7+r(9)
r=7/9
check
7, 7 7/9, 7 14/9, 7 21/9, 7 28/9, 7 35/9, 7 42/9, 7 49/9, 7 56/9, 14
Use the formulas for sum, knowing r, a1 
1st term=7 2nd term=a+d
10term=a+9d
7+9d=2(14+2d)
147=9d2d
7=7d=d=1
sum of 28 term
n/2(2a+(n1)d)
28/2(2*7+(281)1)
14(14+27)=14(41)
25term=574
9th term=7+(91)1
7+(91)
7+8=15
6th term=7+(61)1
7+(61)=7+5=12
9th term6th term=1512=3.