model 4 find nth average from 1st & last number Practice Questions Answers Test with Solutions & More Shortcuts

Answer: (d)

Largest 3–digit number formed by 0, 2 and 4 = 420 Smallest number of three digits = 204

∴ Required average

= ${420+204}/2$ = $624/2$ = 312

Answer: (a)

Using Rule 1,

Average of two or more numbers/quantities is called the mean of these numbers, which is given by

$\text"Average(A)" = \text"Sum of observation / quantities"/\text"No of observation / quantities"$

∴ S = A × n

Sixth number

= 6 × 32 + 6 × 37 – 11 × 35

= 192 + 222 – 385 = 29

Answer: (c)

Using Rule 1,

a + b + c = 45 and

b + c + d = 48

⇒ b + c = 48 – 19 = 29

∴ a + b + c = 45

⇒ a = 45 – 29 = 16

Answer: (b)

Using Rule 1,

Average of two or more numbers/quantities is called the mean of these numbers, which is given by

$\text"Average(A)" = \text"Sumof observation / quantities"/\text"No of observation / quantities"$

∴ S = A × n

Fourth number

= (4×4+4×4 – 3×7)

= (16 +16-21) = 11

Answer: (b)

Using Rule 1,

Average of two or more numbers/quantities is called the mean of these numbers, which is given by

$\text"Average(A)" = \text"Sumof observation / quantities"/\text"No of observation / quantities"$

∴ S = A × n

a + b + c = 18 × 3 = 54

and, b + c + d = 16 × 3 = 48

∴ a + b + c – b – c – d

⇒ 54 – 48 = 6

⇒ a – d = 6

⇒ a – 19 = 6

⇒ a = 19 + 6 = 25