有同样大小的红、白、黑珠共57个，按“二红三白一黑”排列，问这串珠子中共有多少个白珠？+F'X4a8i5I:b:w:I7d3t7p
算式：提示(G6u1\(p;L.v8H2[0F;c3J2_8U4A(Q)}:s6n8d7i+F'X4a8i5I:b:w:I7d3t7p
答：这串珠子中共有;N(F-A'g*a-S(F9E'\.[个白珠。+F'X4a8i5I:b:w:I7d3t7p