model 7 average on ages/weight Section-Wise Topic Notes With Detailed Explanation And Example Questions

Answer: (a)

Total age decreased = 10 × 3 = 30 years.

∴ Age of the retired teacher = 25 + 30 = 55 years.

Aliter : Using Rule 23,

Here, n = 10, x = 3

Age of new teacher = Age of retired teacher – xn

25 = Age of retired teacher – 10 × 3

= Age of retired teacher

= 25 + 30 = 55 years

Answer: (a)

Total age of 5 members, 3 years ago = 17 × 5 = 85 years

Total age of 5 members, now

= (85 + 3 × 5) = 100 years

Total age of 6 members, now

= 17 × 6 = 102 years

∴ Age of the baby

= 102 – 100 = 2 years

Aliter : Using Rule 17,

( 't’ years before, the average age of N members of a family was 'T’ years. If during this period 'n’ children increased in the family but average age (present) remains same, then,

Present age of n children = n.T – N.t )

Here, t = 3, N = 5, T = 17, n = 1

Present age of baby = nT – Nt

= 1 × 17 – 5 × 3

= 17 – 15 = 2 years

Answer: (a)

Easy method:

Average age of new players

= { (20+17)11×$2/12$ }×$1/2$

$422/{12×2}$ =$211/12$⇒ 17$7/12$

= 17 years 7 months

Answer: (b)

A + B + C + D = 20 years

⇒ A + B + D = 20 – 8 = 12 years

Now, A + B + D + E = 24 years

∴ E = 24 – 12 = 12 years

Answer: (a)

Total age of 12 players = 12 × 25 = 300

Total age including captain = 13 × 26 = 338

∴ Age of the captain = 338 – 300 = 38 years

Aliter : Using Rule 23,

( If in a group, one member is replaced by a new member, then,

Age of new member = ( age of replaced member) ± xn

where, x = increase (+) or decrease (–) in average n = Number of members. )

Here, x = 1, n = 12

Age of the captain = Average + x (n + 1)

= 25 + 1 (12 + 1) = 38 years