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In 1950: Ri = 4 Ro -------------- eq1
In 1955: Ri +5 = 3(Ro+5)---------eq2

Thus in 1950, solving eq1 and eq2
Ro= 10 , Ri =40

Now for each year we can calculate:
1960: Ri = 50 , Ro =20
1965: Ri= 55, Ro=25
1970: Ri= 60, Ro = 30

Thus Ans:C
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In 1950 - Rich = 4 * Rob

In 1955 i.e. 5 years later (Rich + 5) = 4 * (Rob + 5) -- here replace the value of Rich as 4*Rob

Age of Rich in 1950 = 40
Age of Rob in 1950 = 10

In YEAR - (Rich,Rob)
In 1950 - (40 ,10),
In 1955 - (45 ,15),
In 1960 - (50 ,20),
In 1965 - (55 ,25),
In 1970 - (60 ,30) - twice

Option C is the correct answer.
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Abhishek009
From the picture above we have 4r+5 = 3r + 15

Or, r = 10

Quote:
In which year was Richard twice as old as Robert?

Let the number of years be " y "

so, 40 + x = 2 ( 10 + x )
Or, 40 + x = 20 + 2x

Or, x = 20

So, After 20 years from 1950 ie 1970 Richard will be twice as old as Robert.

i like your method of solving this question - simple and clean.
one typo though.. Let the number of years be " y " but in your equations, it is x.

thanks again!
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whitehalo
i like your method of solving this question - simple and clean.
one typo though.. Let the number of years be " y " but in your equations, it is x.

thanks again!

Edited , thanks for pointing out !!
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