Step 1: Let Ahmad's pocket money be $a$ dollars. Then Mei Ling originally has $4a$ dollars (she has 4 times as much).\n Step 2: After Mei Ling spends $30, her remaining money is $4a - 30$. Ahmad's money is unchanged at $a$.\n Step 3: The new ratio is $4a - 30 : a = 5 : 2$. Cross-multiply: $2(4a - 30) = 5 \times a$.\n Step 4: Expand: $8a - 60 = 5a$. Rearrange: $8a - 5a = 60$, so $3a = 60$, giving $a = 20$.\n Step 5: Ahmad has $20$ dollars.\nCheck: Mei Ling originally = $4 \times 20 = 80$. After spending $30$, Mei Ling has $50$. Ratio $50 : 20 = 5 : 2$. ✓ Answer: $20