A boy is twice as tall as his little sister and he is 30 cm shorter than his father. The combined height of these three family members is 3.8m. Write an appropriate
equation, using h' as the sister's height and use this to find the boy's height in cm.

Boy = x

His Sister = y

Father = z

x = 2*y  

y = x/2

x = z-30 or z = x+30

3.8 m = 380 cm

x+y+z = 380

x + x/2 + x+30 = 380

multiply by 2

2x +x + 2x +60 = 760

5x = 700

x = 140 cm

y = x/2

 = 140 /2 = 70 cm

z = x+30

 = 140 + 30 = 170 cm

There  

x (Boy)             = 140 cm

y (His Sister)  = 70 cm

z (Father)        = 170 cm

2h= boy

H=girl

2h-30=father

2h+h+2h-30=3.8mthis is the equation

5h-30=3.8m

5h=3.8m-0.30m

5h=3.5m

Divide both sides by 5

H=0.7m

Step-by-step explanation:

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