30 deciliters he already has 1 liter.How many liters of milk will he need to buy?

STEP 1:
find number of liters in 30 deciliters

1 deciliter= 0.1 liter

multiply total number of deciliters (30) by liters in one deciliter (0.1).

=30 * 0.1 liter
=3 liters


STEP 2:
subtract 1 liter from step 1 answer because he already has one liter

= 3 liters - 1 liter
= 2 liters still needed


ANSWER: He needs to buy 2 liters

Hope this helps! :)