Answer:
S₁₅ = 645
Step-by-step explanation:
The sum to n terms of an arithmetic sequence is
= 
[ 2a₁ + (n - 1)d ]
where a₁ is the first term and d the common difference
Using the nth term formula 
= 5n + 3 , then
a₁ = 5(1) + 3 = 5 + 3 = 8
a₂ = 5(2) + 3 = 10 + 3 = 13 , then
d = a₂ - a₁ = 13 - 8 = 5
Thus
S₁₅ = 
[ (2 × 8) + (14 × 5) ]
= 7.5( 16 + 70)
= 7.5 × 86
= 645
Answer:
Step-by-step explanation:
b
Answer:
1
Step-by-step explanation:
Answer:
the answer is x=-1
Step-by-step explanation:
19/25 * 100 = 1900/25 = 76 ....numbers greater then 15
7/50 * 100 = 700/50 = 14....numbers less then 15
100 - (76 + 14) = 100 - 90 = 10 <== numbers equal to 15
