Answer: 6 days
Explanation: If he washes 75 cars in 5 days; and you need to find how many days it takes to wash 90 you do 75 divided by 5 which is 15; so he washes 15 cars in a day, then do 90 divided by 15 which is 6 days
Answer:
First "order of operations" mistake: step 2
First arithmetic mistake: step 4
Step-by-step explanation:
As we understand Rena's work, she wants to simplify ...
for x = -1 and y = 2.
Her work seems to be ...
<u>Step 1</u>
<u>Step 2</u>
<u>Step 3</u>
<u>Step 4</u>
_____
So, the first arithmetic error is in Step 4. However, the order of operations requires exponents be evaluated first. Doing that makes step 2 look like ...
__
We expect your answer is supposed to be Step 4.
Do you remember when you were learning about
Least Common Multiple (LCM) ? And you were
wondering what on Earth you would ever need it for ?
THIS IS IT !
The amount of time after 8 PM when the lights will flash
together again is the LCM of 20 seconds and 30 seconds.
Do you remember how to find it ?
... When 20 is prime-factored, you have 2 · 2 · 5 .
... When 30 is prime-factored, you have 2 · 3 · 5 .
... So the Least Common Multiple of 20 and 30 is 2 · 2 · 3 · 5 = 60 .
The lighthouses will flash together again in 60 seconds after 8 PM.
That'll be 8:01 PM.