Grandfather 7622

My grandfather says, "My son and I are 100 years old, my son and my grandson are 62 years old, and my grandson and I are 80 years old together." How old is your grandfather?

Correct answer:

d =  59

Step-by-step explanation:


d+s = 100
s+v = 62
v+d = 80

d+s = 100
s+v = 62
d+v = 80

Row 3 - Row 1 → Row 3
d+s = 100
s+v = 62
-s+v = -20

Row 3 + Row 2 → Row 3
d+s = 100
s+v = 62
2v = 42


v = 42/2 = 21
s = 62-v = 62-21 = 41
d = 100-s = 100-41 = 59

d = 59
s = 41
v = 21

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