Brain Teaser: Maths Qn

[Hobbiez]

Braun and Catherine weigh 51kg. Joan and Braun weigh 81kg. Braun is 3 times heavier than Catherine. What is their total average weight?

[Yc86]

31.25kg?

[Requiemdk]

b + c = 51 - (1)

b + j = 81 - (2)

 

Adding them, 2b + j + c = 132 (3)

 

Since b = 3c, this is just b + j + 4c = 132 (3a)

 

Adding 3 times of (2) to (3a), 4b + 4j + 4c = 375 (4)

 

Dividing (4) by 12, we have (1/3)(b + j + c) = 31.25. This is their average weight.

[Freestylers09]

2nd that...haha

[Mivec9]

Braun = 3 Units

Catherine = 1 Units

 

81 - 51 = 30kg

Hence 2 Units = 30kg

1 Unit = 15kg (Catherine)

3 Units = 45kg (Braun)

So Joan = 81 - 45 = 36kg

 

Avg = (15 + 45 + 36) / 3 = 32kg

[Comfy]

underweight?

[Hobbiez]

Clue: (3+1)U = 51kg

 

Congratulations to those who got 31.25kg

[Garlic]

X + 3X = 51

Therefore X = 12.75

 

As such,

Braun -> 38.25

Catherine -> 12.75

Joan -> 42.75

 

Therefore mean weight is 31.25kg , [(38.25)+(12.75)+(42.75)] / 3

[Driven]

mine has the same calculation as you. Wonder if its the right method?