Add the decimals: align the decimal points.
• 12.46 + 9.78
• 6 + 8 = 14 hundredths: write 4, carry 1 to tenths
• 4 + 7 + 1(carry) = 12 tenths: write 2, carry 1 to ones
• 2 + 9 + 1(carry) = 12 ones: write 2, carry 1 to tens
• 1 + 0 + 1(carry) = 2 tens
• 12.46 + 9.78 = 22.24
Final Answer: 22.24