I need to find the sum of 2/5 and 3/4. The LCD is 20 so I did 2x4=8 and 3x5=15. so I got 8/20 + 15/20 = 23/20, but this does not match any of the answers I have to pick from. What am I doing wrong?
2/5 + 3/4 = 8/20 + 15/20 = 23/20 = 1.15
you are correct. answer key is bogus
unless it had 1.15 as an answer
or, 1 3/20
The steps you followed to find the LCD and convert the fractions to a common denominator are correct. However, it seems like you made an error in the addition of the fractions.
To add 8/20 and 15/20, you simply add the numerators (8 + 15 = 23) while keeping the denominator the same (20). So the correct sum is 23/20.
It's possible that the given answer choices are not in simplified form. To verify, you should check if 23/20 can be further simplified.
To find the sum of fractions, you correctly identified that you need to find a common denominator (also called the Least Common Denominator or LCD). In this case, the LCD is indeed 20 because it is the smallest multiple that both 5 and 4 have in common.
You then multiplied the numerator and denominator of the first fraction (2/5) by 4, and the second fraction (3/4) by 5 to make their denominators match the LCD:
2/5 = 2 x 4 / 5 x 4 = 8/20
3/4 = 3 x 5 / 4 x 5 = 15/20
At this point, you correctly rewrote the fractions with the common denominator. However, you made a mistake in the next step. Instead of adding the numerators directly, you should add the fractions together by keeping the denominators the same:
8/20 + 15/20 = (8 + 15) / 20 = 23/20
So, 23/20 is the correct sum of 2/5 and 3/4. If none of the provided answer options match 23/20, it's possible that you made an error in transcribing the answers, or there may be a mistake in the answer choices. Double-check your work and consider reaching out for clarification if needed.