Question

In an ap given a=5 d=3 an=50 find n and S​

Answer 1

Answer:

We have, a= 5, d=3 and an=50

> a+(n-1)d= 50

> 5+(n-1)3=50

> 3(n-1)=50-5

> n-1 = 45/3

> n-1 = 15+1 = 16

Putting n = 16, a= 5 and l = an = 50 in Sn= n/2(a+l),

We get

S16 = 16/2( 5 + 50) = 8 × 55 = 440

Hence, n= 16 and S16 = 440

Answer 2

Gɪᴠᴇɴ :

• a = 5
• d = 3
• an = 50

Tᴏ Fɪɴᴅ :

• n and Sn

Sᴏʟᴜᴛɪᴏɴ :

an = a + (n - 1) d = 50

⇒ 50 = 5 + (n - 1) 3

⇒ 50 - 5 = 3n - 3

⇒ 3n = 45 + 3

⇒ n = 48/3

⇒ n = 16

Sn = n/2 [a + l]

⇒ S16 = 16/2[5 + 50]

⇒ S16 = 8 × 55

⇒ S16 = 440