Math Question

[jirotrom]

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Donna says that she was 21 when her daughter Trish was born. But when asked how old her daughter is today, Donna states that in 6 years she'll be 6 more than twice her daughters age. how old is donna's daughter, Trish?

I used this equation:
D= Donna, T= Trisha

D= T+21

D+6= 2(T)+6

I solve and get 21, but its wrong... can someone please explain 😀

 

[herkulease]

Is the answer 9 years old?

 

[jirotrom]

Is the answer 9 years old?

yes it is but why... I know Im making a silly oversight, as its probably that my mind isn't realizing my mistake yet.

 

[DeathNote]

Donna says that she was 21 when her daughter Trish was born. But when asked how old her daughter is today, Donna states that in 6 years she'll be 6 more than twice her daughters age. how old is donna's daughter, Trish?

I used this equation:
D= Donna, T= Trisha

D= T+21

D+6= 2(T)+6

I solve and get 21, but its wrong... can someone please explain 😀

Second equation is wrong:
D=T+21
D+6=2(T+6)


So D=2T+6 from second equation. Plug into first equation and you get:

2T+6=T+21, you solve and get T=15 (this number is 6 years from the current age, so subtract 6 years and, voila, you get Trish=9 years old)

 

[LuckMC11]

i think you do D = 2T + 6 + 6, because it is saying in 6 years, so you would just add it at the end, so then D = 2T + 12. then you plug in for D in the first equation, so
D=T +21 turns to 2T + 12 = T + 21. Solve for T, done.

 

[herkulease]

deathnote set it up like how did. so yeah.

Ok I think I see what hte problem with your set up.

In your set up

D+6= 2(T)+6

If mom goes up by X years, daughter has to go up by the same amount. here the daughter doesn't age.

 

[DeathNote]

Donna says that she was 21 when her daughter Trish was born. But when asked how old her daughter is today, Donna states that in 6 years she'll be 6 more than twice her daughters age. how old is donna's daughter, Trish?

I used this equation:
D= Donna, T= Trisha

D= T+21

D+6= 2(T)+6

I solve and get 21, but its wrong... can someone please explain 😀

I find that the best way to do these problems is to just plug in the answers and not solve out using equations--the hardest part of this section is the time and these questions take some time to comprehend.

 

[jirotrom]

deathnote set it up like how did. so yeah.

Ok I think I see what hte problem with your set up.

In your set up

D+6= 2(T)+6

If mom goes up by X years, daughter has to go up by the same amount. here the daughter doesn't age.

why? I added the 6 so she does age... confused🙁

 

[Chemwiz]

why? I added the 6 so she does age... confused🙁

in 6 years, donna will be D+6 and trish will be T+6. so D+6=2(T+6)+6 is correct.

 

[jirotrom]

in 6 years, donna will be D+6 and trish will be T+6. so D+6=2(T+6)+6 is correct.

Why 2(T+6)6 instead of just 2(T)+6?

 

[Streetwolf]

Why 2(T+6)6 instead of just 2(T)+6?

Twice her age in 6 years is 2(T+6) not 2T + 6.

Remember that you are not only doubling her age (T) but you are doubling the extra 6 years added on.

If she was 10 years old, then double her age in 6 years (16) is 32 --> 2(10+6), not 26 --> 2(10) + 6.

Add the 6 on the left (mother's age) because it's 6 years later. Add the extra 6 on the right because the mom is 6 years older than double the daughter's age at that time.

 

[jirotrom]

Twice her age in 6 years is 2(T+6) not 2T + 6.

Remember that you are not only doubling her age (T) but you are doubling the extra 6 years added on.

If she was 10 years old, then double her age in 6 years (16) is 32 --> 2(10+6), not 26 --> 2(10) + 6.

Add the 6 on the left (mother's age) because it's 6 years later. Add the extra 6 on the right because the mom is 6 years older than double the daughter's age at that time.

Oh!
i was comprehending it incorrectly😀 thanks so much!