the average height 15 boys and 20 girls in a class is 1.5 meter. the average height of girls is 1.45 meters. what is the average height of t

average height of class = (15*b + 20*g)/(15+20) where b is average height of boys and g is average height of girls.

 

So  1.5 = (15b + 20*1.45)/35

 

Multiply both sides by 35

35*1.5 = 15b + 20*1.45

 

Subtract 20*1.45 from both sides

35*1.5 - 20*1.45 = 15b

 

Divide both sides by 15

b = (35*1.5 - 20*1.45)/15

$${\mathtt{b}} = {\frac{\left({\mathtt{35}}{\mathtt{\,\times\,}}{\mathtt{1.5}}{\mathtt{\,-\,}}{\mathtt{20}}{\mathtt{\,\times\,}}{\mathtt{1.45}}\right)}{{\mathtt{15}}}} \Rightarrow {\mathtt{b}} = {\mathtt{1.566\: \!666\: \!666\: \!666\: \!666\: \!7}}$$

 

or the average height of the boys is approximately 1.57m

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