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

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: (b)

Average age of 4 brothers = 12 yrs.

Total age of 4 brothers = 4 × 12 = 48 yrs.

Average age of 4 brothers + mother ( = 5 persons) = 12 + 5 = 17 yrs.

∴Total age of 4 brothers + mother = 5 × 17 = 85 yrs.

∴The age of the mother = 85 – 48 = 37 yrs.

Aliter : Using Rule 24,

( If a new member is added in a group then. age (or income) of added member = Average (or income) ± x (n + 1)

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

Here, x = 5, n = 4

Age of mother = Average+x (n+1)

= 12 + 5 (4 + 1)

= 12 + 25 = 37 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