Question

In a mathematics exam, a student multiplied a number by 9/10 instead of dividing the number by
9/10. How much percent error will be there in answer?​

Answer 1

Explanation:

Correct option is

B

64%

Let the number be x.

Then, percentage error =

⎝

⎜

⎜

⎛

3

5

x

3

5

x−

5

3

x

⎠

⎟

⎟

⎞

×100%=

3

5x

15

25x−9x

×100%

=

15

16x

×

5x

3

×100%=64%.

Answer 2

Given:

A number

To find:

Per cent error

Solution:

The required per cent of error is 19%.

Let us assume that the number is 90.

We know that the student has multipled it by 9/10 instead of dividing.

So, the wrong number obtained=number×9/10

Using the values,

=90×9/10

=81

Now, we have to divide the number by 9/10.

So, the correct number obtained=90/(9/10)

=90×10/9

=100

We know that the error made=correct value-wrong value

=100-81

=19

The per cent required=error/correct value×100

=19/100×100

=19%

Therefore, the required per cent of error is 19%.