The fraction of the peanut butter that Irfan used that was less than the amount he should have used was 1/10.
Irfan was meant to use 1/2 cups of peanut butter but instead used only 2/5.
The amount that he didn't use was therefore:
= 1/2 - 2/5
In decimals this is:
= 0.5 - 0.4
= 0.1
In fraction form this:
= 10/100
= 1/10
Find out more on fractions at https://brainly.com/question/15548065.
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