All categories

3 years ago

Four brothers and their sister have the average age 7. Four brothers have the average age 6. How old is the sister?

Mathematics

1 answer:

AnnyKZ [126]3 years ago

4 0

Answer:

11 years old

Step-by-step explanation:

If four brothers have the average age 6, then the sum of their ages is

$4\cdot 6=24$

years.

Let x years be the age of sister. If four brothers and their sister have the average age 7, then

$\dfrac{24+x}{5}=7.$

Multiply this equation by 5:

$24+x=35\Rightarrow x=35-24=11.$

The sister is 11 years old.

You might be interested in

A) make U subject of the formula E= m/2g(v^2-u^2)

ollegr [7]

Answer:

u = v2−2Egm−−−−−−−√

Step-by-step explanation:

2Eg = 2g (M2g(V2−U2)

2Eg = m(V2 - U2)

2Eg - mV2 - mU2

mU2 = mV2 - 2Eg

mU2m=mV2−2Egm

U2 = mV2−2Egm

= mV2m−2Egm

U2 = V2 - 2Egm

U = V2−2Egm−−−−−−−−√

7 0

2 years ago

the diffrence of two numbers,a and b,is 21,the diffrence of five times a and two times b is 18 what are the values of a and b

Triss [41]

Answer:

a=-8

b=-29

Step-by-step explanation:

Let's assume

first number is a

second number is b

the difference of two numbers,a and b,is 21

so, we get

$a-b=21$

we can solve for 'a'

$a=b+21$

the difference of five times a and two times b is 18

so, we get

$5a-2b=18$

now, we can plug 'a'

$5(b+21)-2b=18$

now, we can solve for b

$5b+105-2b=18$

$3b+105=18$

$3b=-87$

$b=-29$

now, we can find 'a'

$a=-29+21$

$a=-8$

8 0

2 years ago

Read 2 more answers

Find x. Round to the nearest tenth: y 31° X 400 ft x = ? ]ft

Ludmilka [50]

A = 31 degree
Cos 31 degree = 400/x
X = 400/ Cos 31
= 400/0.8572
= 466.7ft

4 0

1 year ago

Plsss help ASAP !! giving the brainlest answer to whoever can help me out?? plsss

timofeeve [1]

Answer:

The 2nd one

Step-by-step explanation:

6 0

2 years ago

There are currently 73 million cars in a certain country, decreasing by 1.7% annually.

Olin [163]

Answer:

17.6 years

Step-by-step explanation:

There are currently 73 million cars in a certain country, decreasing by 1.7% annually.

How many years will it take for this country to have 54 million cars? Round to the

nearest year.

We use the formula

y = a(1 - r)^t

a = Initial amount = 73 million cars

y = Future amount = 54 million cars

r = decreasing rate = 1.7 % = 0.017

t = time is unknown

54,000,000 = 73,000,000(1 - 0.017)^t

Divide both sides by 73,000,000

54,000,000/73,000,000 = (0.983)^t

0.7397260274 = (0.983)^t

Take the logarithm of both sides

log 0.7397260274 = Log (0.983)^t

log 0.7397260274 =t log (0.983)

t = log 0.7397260274/log 0.983

t = -0.13092910029/-0.00744648216

t = 17.5826783005 years

Approximately = t = 17.6 years

7 0

2 years ago