The average salary of all staff of a school is ₹10000. The average salary of 20 teaching staff is ₹12000 and that of non-teaching staff is ₹5000. The number of non-teaching staff will be :

8

The average salary of all staff of a school = ₹10,000

Let Number of non-teaching staff = n

∴ 20 × 12000 + n × 5000 = (n + 20) × 10000

⇒ 240000 + 5000n = (n + 20) × 10000

⇒ 240 + 5n = (n + 20) × 10

⇒ 10n – 5n = 240 – 200

⇒ 5n = 40

⇒ n = \(\frac{40}{5}\) = 8