Notam cu x suma initiala.
1/3*x + 2/7 (x-x/3) +150 =x ==> x/3+2x/7-2x/21 + 150 = x ==> (aducem primii trei termeni la acelasi numitor comun) 7x+6x-2x totul supra 21 +150 =x ==> 11x/21 + 3150/21 = 21x/21 ==> 11x+3150=21x ==> 10x=3150==> x=315. Prima data a cheltuit 1/3 * 315 = 105. A doua oara a cheltuit 2/7 * (315-105) = 2/7 * 210 = 60.