3A+2B=20
2A+B=13 ➡×(-2)➡-4A-2B=-26
3A+2B-4A-2B=20-26
-A=-6 ➡A=6
2(6)+B=13➡B=1
Sn = n/2(a + l); where sn is the sum of n terms, n is the number of terms, a is the first term and l is the last term.
1390 = n/2(3 + 136)
2780 = 139n
n = 2780/139 = 20
2nd term = 3 + 20 = 23
3rd term = 23 + 20 = 43
First three terms = 3, 23, 43
option b.
Answer:
-10
Step-by-step explanation:
5 is lower than 15 so the answer must be negative
if 15 minus 5 is 10
then 5 minus 15 has to be 10
