Let us assume the number be N.
According to question,
A number when subtracted by 1/7 of itself gives the same value as the sum of all the angles of a triangle,
N - N x 1/7 = 180 ( As we know sum of all angels of a triangle is 180 .)
⇒ N - N/7 = 180
⇒ (7N - N)/7 = 180
⇒ (7N - N) = 180 x 7
⇒ 6N = 180 x 7
⇒ N = 180 x 7/6
⇒ N = 30 x 7
⇒ N = 210
