fast problem solving qn (1 Viewer)

[ronaldinho]

My father is 24 years odelr than me, and 12 years ago he was double my age. How old am i now?

 

[ianc]

Let my current age be x, father's current age be y

therefore
y-x=24
y-12=2(x-12)

Solve simultaenously

 

[PC]

My father is 24 years odelr than me, and 12 years ago he was double my age. How old am i now?

Simultaneous equations can work, but aren't needed.

Let x be my age now, so my father is (x + 24).
12 years ago my age is (x – 12) and my father is twice this so 2(x – 12).

Since the difference in ages is always the same,
(x + 24) – x = 2(x – 12) – (x - 12)
x + 24 – x = 2x – 24 – x + 12
24 = x – 12
x = 36

I am 36, my father is 60.
12 years ago I was 24 and my father was 48.

 

[ronaldinho]

Why did you subratct them?

x-24-x...

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A fuel tank is 40 percent full. When added 28L it becomes 75 percent full. How many litres can the tank hold?

 

[PC]

Why did you subratct them?

x-24-x...

The difference between two people's ages is always the same.

 

[watatank]

A fuel tank is 40 percent full. When added 28L it becomes 75 percent full. How many litres can the tank hold?

Let the volume of a full fuel tank be x

0.4x + 28 = 0.75x

(2/5)x + 28 = (3/4)x

Eliminate denominator

20.(2/5)x + 20.28 = 20.(3/4)x

8x + 560 = 15x

7x = 560

x = 80

Hence a full fuel tank can hold 80L

:wave:

 

[PC]

Who needs algebra!

When the tank has 28 litres added it goes from 40% full to 75% full, or it goes up by 35%.

This means that 35% of the tank is equal to 28 litres.

35% of tank = 28 litres
Now divide by 7
5% of tank = 4 litres
Now multiply by 20
100% of tank = 80 litres

.: Tank can hold 80 litres.