A man has in all Rs. 640 in the denominations of one-rupee, five-rupee and ten-rupee notes. The number of each type of notes are equal. What is the total number of notes he has?

\[\begin{array}{*{20}{c}} {}&{{\text{Rs}}{\text{. 1}}}&:&{{\text{Rs}}{\text{. 5}}}&:&{{\text{Rs}}{\text{. 10}}}&{} \\ {{\text{Number of notes}}}&1&:&1&:&1&{} \\ {}&x&:&x&:&x&{ = \boxed{3x}{\text{ number of notes}}} \\ {{\text{So, Value}}}&x&:&{5x}&:&{10x}&{ = \boxed{16x}{\text{ value of notes}}} \end{array}\]
$$\eqalign{ & x + 5x + 10x = 640 \cr & 16x = 640 \cr & \boxed{x = 40} \cr & \therefore {\text{Number of notes }}40 \times 3 = 120 \cr} $$