*Rohan has a stationery collection, consisting of rulers, pens and erasers. His pencil box has a total of 20 pieces. Rohan as two and half times as many rulers as pens, and the number of erasers is 4 less than the number of rulers. How many erasers does Rohan have?*

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Assume that there are R rulers, P pens and E erasers. It is given that:
R = (5/2) * P or P = (2*R)/5
And, the number of pairs of erasers is 4 less than the number of rulers.
E = R – 4 or R = E + 4
Also, combining the above, we have P= {2*(E+4)}/5
Also, there are total 20 pieces.
R + P + E = 20
{2*(E+4)}/5+E+4+E= 20
Multiply both sides by 5 and carrying out the necessary operations, we have
12E+28= 100
E = 6
Therefore, Rohan has a total of 6 erasers.

6……………..

4 pens, 10 rulers, 6 erasers

rohan has 6 erasers.

Rohan has 6 erasers, 10 rulers and 4 pens.