The average weight of a class of 15 boys and 10 girls is 38.4 kg. If the average weight of the boys is 40 kg, then what is the average weight of the girls?

Here, n₁ = 5, n₂ = 10, n₃ = 15, a₁ = 25, a₂ = 50, a₃ = 35
According to the formula,
Average price = (n₁a₁ + n₂a₂ + n₃a₃) / (n₁ + n₂ + n₃)
= (5 x 25 + 10 x 50 + 15 x 35) / (5 + 10 + 15)
= (25 + 100 + 105) / (1 + 2 + 3)
= 230/6
= ? 38.33

Let The total number of workers = N
According To the question,
60N = 12 x 400 + 56 (N - 12)
? 60N - 56N = 4800 - 672
? 4N = 4128
? N = 1032

47(a + b) = 5452
? a + b = 5452/47 = 116
? Average value = (a + b)/2
= 116/2
= 58

According to the question,
70m + 91n = 80 (m + n)
⇒ 70m + 91n = 80m + 80n
⇒ 10m = 11n
⇒ n/m = 10/11

Let the 5 consecutive positive integers be x + 1, x + 3, x + 5, x + 7, x + 9
Average = (Sum of all terms) / (Number of terms)
⇒ 9 = [(x + 1) + (x + 3) + (x + 5) + (x + 7) + (x + 9)]/5
⇒ 9 = (5x +25)/5
⇒ 45 = 5x + 25
⇒ 5x = 45 - 25
∴ 5x = 20 ⇒ x = 4
The least one is x + 1 = 4 + 1 = 5

Here n = 120, a = 35, x = 39, y = 15
Number of students passed = n (a - y)/(x - y)
= 120(35 - 15)/(39 -15)
= 100 students passed

If two equal distance are covered at different speeds at A km/h and B km/h respectively, then
Average speed during the whole journey = 2AB/(A + B) km/h

? Average speed of the car = (2 x 42 x 48) / (42 + 48)
= (2 x 42 x 48)/90
= 44.8 km/h

Let one integer be x.
? Other ingeger x + 15
According to the question,
29 + x + x + 15+ 108 = 4 x 73.5
? 2x + 152 = 294
? 2x = 294 - 152 = 142
? x = 142/2 = 71

Let average of a inning = x
Total runs = 9x
According to the question,
(9x + 100) /10 = x + 8
? 9x + 100 = 10x + 80
x = 20
Average after 10 inning = 20 + 8 = 28

Total age of 5 memeber (3 yr ago) = 27 x 5 = 135 yr
Total age of 5 members (at present) = 135 + 5 x 3 = 150 yr.
Let the persent age of child = x
? 27 = (150 + x)/6
? x = 162 - 150 = 12 yr.