How much is -3 1/5 + 12 3/8?

You need to first get a common denominator.

12 3/8 = 12 15/40
3 1/5 = 3 8/40

12 15/40 - 3 8/40 = ?

so the answer is 9 7/40

Right.

To add mixed numbers like -3 1/5 and 12 3/8, follow these steps:

Step 1: Convert the mixed numbers to improper fractions.
To convert a mixed number to an improper fraction, multiply the whole number by the denominator and add the numerator. Then write the result over the original denominator.

-3 1/5 = (-3 × 5 + 1) / 5 = (-15 + 1) / 5 = -14/5

12 3/8 = (12 × 8 + 3) / 8 = (96 + 3) / 8 = 99/8

Step 2: Find a common denominator.
To add or subtract fractions, you need to find a common denominator. In this case, the common denominator for 5 and 8 is 40.

Step 3: Rewrite the fractions using the common denominator.
Multiply the numerator and the denominator of each fraction by the same factor so that both fractions have the same denominator.

-14/5 = (-14 × 8) / (5 × 8) = -112/40

99/8 = (99 × 5) / (8 × 5) = 495/40

Step 4: Add the fractions.
Add the numerators and keep the common denominator.

-112/40 + 495/40 = (-112 + 495) / 40 = 383/40

Step 5: Simplify (if required).
If needed, simplify the resulting fraction. In this case, 383/40 cannot be simplified further.

So the sum of -3 1/5 and 12 3/8 is 383/40.