The number of boys to girls in math class is 2:3 If there are 21 girls in Mrs. Vest's math class, how many boys are there? Can w
2 answers:
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Answer:
Step-by-step explanation:
Let's start with the first problem :
- Dora spent 1/3 of her money and it equals 72
- Jack spen 1/4 and had the amount left
To get the initial amount that Dora had we must multliply 72 by 3 since she spent 1/3 and 3 is the total number of parts
- 72*3=216 ⇒ Dora had 216
- she spent 72 so : 216-72=144 ⇒144 is the amount left for her and Jack
Jack spent 1/4 of his total amount and had 144 left
- 144 is 3/4
- to get 1/4 we must divide 144 by 3 ⇒ 144/3=48
- so the total amount is 48*4=192
Let's check : 192-48= 144 so it's right
- Jack spent 48
The second question :
We notice that the total area A is the sum of the white square's area and the blue region's area
- A= 65+ x x is the area of the white square so x = 4*4 since it is 4cm*4cm
- so A= 65+16= 81
- we khow that the area of a square is the lenght times itself
- so 81 = y² with y the lenght of the large blue square and y≥0 since it is a distance
- y=
= 9
- so the lenght is 9 cm
The third problem :
- Mo gave alex some stickers and now he has twice as many as Mo
- Mo had 150 and Alex 207
- so let x be the amount of stickers we are locking for
- then : 207 +x = 2(150-x)
- 207+x = 300-2x
- 207 +3x = 300
- 3x = 300-207 ⇒93= 3x ⇒ x= 31
Let's check : 150-31 = 119 119*2= 238
207 + 31 = 238 that's right
so mo gave 31 stickers to alex