Free Primary School Maths Help - You Post I Solve!

[kiasiparent]

When Mrs Lee was 40 years old, her son was twice her daughter’s age. Mrs Lee will be twice her son’s age when her daughter is 28 years old. How old will Mrs Lee be when her daughter is 20 years old?

[fridayeducation]

kiasiparent:

When Mrs Lee was 40 years old, her son was twice her daughter's age. Mrs Lee will be twice her son's age when her daughter is 28 years old. How old will Mrs Lee be when her daughter is 20 years old?

Mrs Lee will be 56 years old when her daughter is 20 years old. I've just got back and had done this by logic and guess & check. perhaps you'll like to let me know what level is your child or is this question intended for so i can prepare a solution catered to the understanding of the level? Thanks.

[fridayeducation]

suiyuan:

Thank you for your offer.You may want to help to answer the following questions.

1)Car A and Car B left Town Y at the same time heading in the opposite directions. Car A headed for Town Z while Car B left for Town X. The speed of Car B was 20 km/h faster than Car A. After 1/2 h, Car A had completed 2/3 of its journey while Car B had completed 1/2 of its journey. The two cars were also 110 km apart.(a) Calculate the speed of Car A (b) How far was Car B from Town X when car A reached its destination?

(a) Calculate the speed of Car A

Step 1: State Formuala,

Using Distance = Speed x Time,

Step 2: Equation
110km = 1/2 x (Total Speed)
220km/h = Total Speed (Total speed refers to combined speed of Car A and Car B)
\t= A's Speed + B's Speed
\t= A's Speed + A's Speed + 20km/h
200km/h = 2 (A's Speed)
100km/h = A's Speed

(b) How far was Car B from Town X when car A reached its destination?

Step 1: State Formular (Always state formula - not for marks, in case you forget)
Using Distance = Speed x Time

Since Car A,

Time taken to complete 2/3 journey - 1/2 hour
Time taken to complete remaining 1/3 journey - 1/2 hour / 2 = 1/4hour

Car B

Car B's Speed - 100km/h + 20km/h = 120km/h
Distance Car B will travel in 1/4hour - 120 km/h x 1/4h = 30km
Distance from Town Y to Town X - 60km x 2 = 120km
Distance Car B will be from Town X - 120km - 60km - 30km = 30km

[fridayeducation]

suiyuan:

2)Mr Lee and Mr Tan both drove from Town X to Town Y. Mr Lee started his journey at 10.00 am travelling at an average speed of 75 km/h. Sometime later, Mr Tan started his journey. At 12.00 noon, Mr Tan overtook Mr Lee. When Mr Tan reached Town Y at 2.00 pm, Mr Lee was still 50 km from Town Y. Find (a) Mr Tan's average speed (b) The time at which Mr Tan started his journey

Notes (Good to have)

Lee\t10am\t75km/h

Tan \tovertook at 12pm\treached at 2pm

(a) Mr Tan's average speed

Using Formala, Distance = Speed x Time

At 12pm, Lee travelled - 75k/h x 2h = 150km
At 2pm, Lee travelled - 75km/h x 4h = 300km

Distance between town X and Town Y - (75km/h x 4h) + 50km = 350km
(Reasoning - At 2pm, 4 hours after Lee left Town X, he is still 50km away from Town Y)

At 12pm they met and within 2 hours, Tan reached and Lee is still travelling, in fact we know that Lee is now 50km away. Can we find out Tan's speed now?

Distance Tan travelled between 12pm and 2pm (2hours) - 75km/h x 2h + 50km = 200km
Tan's average speed - 200km / 2h = 100km/h

(b) The time at which Mr Tan started his journey

Using Formala, Distance = Speed x Time
Total time taken for time to reach Town Y from Town X - 350km / 100km/h = 3.5h
Time Tan started his journey - 1400h/2pm - 3h30min = 1030h or 1030am

[fridayeducation]

suiyuan:

3)Town A and Town B were 600 km apart. At 10.45 am, a lorry travelling at a uniform speed left Town A for Town B. At the same time, a taxi set off from Town B to Town A at a uniform speed which was 12 km/h faster than that of the lorry's. The two vehicles met at 3.45 pm. Find the speed of the taxi.

The concept of this concept is the same as that of question 1. Distance and time is provided in this question and then one vehicle is faster than another. In this question, time is provided when they state time vehicles set off and time they met. It is all the same.

As long as DISTANCE & TIME are the given AND they are comparing 2 vehicle's speed (coming/going in opposite direction), this is how you should solve, remember that TOTAL SPEED in this case includes speed for both lorry and taxi.

Using Formula, Distance = Speed x Time

600km = 5h (Total Speed)
120km/h = Total Speed
\t= Lorry's Speed + Taxi's Speed
\t= Lorry's Speed + Lorry's Speed + 12km/h
108km/h = Lorry's Speed + Lorry's Speed
54km/h \t= Lorry's Speed

Taxi's Speed - 54km/h + 12km/h = 66km/h

(To check, always check)

They both travelled 5hours and they met, so the distance they've travelled must add up to distance given, 600km

Lorry's Distance - 5h x 54km/h = 270km
Taxi's Distance - 5h x 66km/h = 330km
Total Distance - 270km + 330km = 600km

[suiyuan]

fridayeducation:

kiasiparent:

When Mrs Lee was 40 years old, her son was twice her daughter's age. Mrs Lee will be twice her son's age when her daughter is 28 years old. How old will Mrs Lee be when her daughter is 20 years old?

Mrs Lee will be 56 years old when her daughter is 20 years old. I've just got back and had done this by logic and guess & check. perhaps you'll like to let me know what level is your child or is this question intended for so i can prepare a solution catered to the understanding of the level? Thanks.

Hi
This is a question from P6.

[corneyAmber]

kiasiparent:

When Mrs Lee was 40 years old, her son was twice her daughter's age. Mrs Lee will be twice her son's age when her daughter is 28 years old. How old will Mrs Lee be when her daughter is 20 years old?

You can find the answer here:

http://madabtmath.wordpress.com/2008/10/23/p6-math-momdsdd-age/

[suiyuan]

Hi

fridayeducation

Thank you for your answers.

[acforfamily]

suiyuan:

2)Mr Lee and Mr Tan both drove from Town X to Town Y. Mr Lee started his journey at 10.00 am travelling at an average speed of 75 km/h. Sometime later, Mr Tan started his journey. At 12.00 noon, Mr Tan overtook Mr Lee. When Mr Tan reached Town Y at 2.00 pm, Mr Lee was still 50 km from Town Y. Find (a) Mr Tan's average speed (b) The time at which Mr Tan started his journey

Hi, can it be done this way without finding the total distance.

(a)\tMr Tan’s average speed

Using Formula, Distance = Speed x Time
Distance travelled by Lee in the same time from 12 noon to 2 pm = 75km/h *2h = 150 km
Since Lee is 50 km away from town Y, Tan would have travelled 150km+50km = 200km in the same time

Using Formula, Speed = distance / Time
Tan’s speed = 200 km / 2 h = 100 km/h

(b)\tTime that Tan started
Distance that Lee has travelled before Tan overtook him = 75km/h*2h = 150 km
Using Formula, time = Distance / Speed

Time taken for Tan to overtake him = 150 km / 100 km/h = 1.5 hours
Which means 12 noon less 1.5 hours, that would be 10.30 am that he started

[fridayeducation]

acforfamily:

Hi, can it be done this way without finding the total distance.

(a)\tMr Tan’s average speed

Using Formula, Distance = Speed x Time
Distance travelled by Lee in the same time from 12 noon to 2 pm = 75km/h *2h = 150 km
Since Lee is 50 km away from town Y, Tan would have travelled 150km+50km = 200km in the same time

Using Formula, Speed = distance / Time
Tan’s speed = 200 km / 2 h = 100 km/h

(b)\tTime that Tan started
Distance that Lee has travelled before Tan overtook him = 75km/h*2h = 150 km
Using Formula, time = Distance / Speed

Time taken for Tan to overtake him = 150 km / 100 km/h = 1.5 hours
Which means 12 noon less 1.5 hours, that would be 10.30 am that he started

Yupp! Your answer is shorter and more direct than me. Thanks for sharing!