Question

if the first term and last term of an AP are 10and 15 respectively. what will be the number of terms in it if there sum is 125 ?​

Answer 1

Given:

• The first term (a) = 10
• The last term (l) = 15
• Sum = 125

To find: The number of terms in the AP.

Answer:

We know that:

$\tt Sum\ =\ \dfrac{n}{2}\ \times\ \bigg(a\ +\ l\bigg)$, where 'n' is the number of terms in the AP.

[This can only be used if you know the first and last terms.]

Using the values we have,

$\tt 125\ =\ \dfrac{n}{2}\ \times\ \bigg(10\ +\ 15\bigg)\\\\\\250\ =\ n\ \times\ 25\\\\\\\dfrac{250}{25}\ =\ n\\\\\\10\ =\ n$

Therefore, there are 10 terms in the AP.

Answer 2

Answer:

n=

Step-by-step explanation:

a=10

an=15

sn=125

sn=n/2(a+an)

125=n/2(10+15)

125×2=n×25

250=n25

n=250/25

n=10