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6. Each of Rinku, Tiya and Abir are asked to choose three numbers so that the sum of the third and the first number is twice the second one and the third number is $2$ greater than the second number. It was observed that the second number of Rinku is $2$ smaller than the second number of Tiya and the second number of Tiya is $2$ smaller than the second number of Abir. If the third number chosen by Tiya is $15$, find the first number chosen by Abir.

The first number chosen by abir is 13

but how u get the ans ?

CONDITION, X1 + X3 = 2 X2 and X3 = X2 + 2. GIVEN : Xr2 = Xt2 -2, Xt2= Xa2-2, Xt3= 15, Xa1=?
X1 = X2 -2,
NOW, FROM 2nd con., Xt2 = 15-2=13. Xa2= Xt2+2=13+2=15. Xa1= Xa2-2=15-2=13.