It is known that when a word needs to be changed to past tense we just need to add "ed" at the end of it as a suffix. However there are certain rules to follow, in this case, the rule is to<u> change the "Y" to an "I"</u>. <u>This rule is applied when the word has a consonant before the "Y", in this case, the "Y" must be replaced with an I and then the suffix "ed".</u>
