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easy Digits problem and Semicircle.. - fastest way to solve it? Otherwise easy

Hello

im not sure what the fastest way to solve this is..

please let me know.. thanks!

22. A and B are letters representing different digits from 1 to 9.

Given:

AB

X 7

-----

4BB

A-B=?

(I) 1

(2) 2

(3) 3

(4) -1

answer: 1

need 5 bc 7*5= 35.. b needs to be 5.

..

defiitely 5.

definitely need a 6 because 60 * 7 is 420 ish..

7 is too high

..

so 6-5 =1

not sure if this is the fastest way! thanks!

21.

A certain 2 digit number is known to be 3 times as great as the sum of its digits. What is the product of its digits?

1. 12

2. 14

3. 16.

4. 18

answer: 2

27 is 3x greater than 2+7 = 9.

2*7 is 14.

not sure how to do this FAST without going backwards?(Rock)

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Semicircle.. shaded region

q21

the legs of a triangle ABC are 2 and 4. it is in a semicircle. and is painted white. the rest of the semicircle is black. what is the area of the black?

i know that answer must have -4 because 1/2 * 2 * 4 = 4.

the area..

2^2 + 4^2 = hyp^2

4 + 16 = 20, hyp is root 20

pi* (1/2 root 20 )^2 = total area.

20/4 = 5

so 5pi - 4??

huh

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PS is there a way to post pictures up here? other people did it and i'd like to know how!

Re: easy Digits problem and Semicircle.. - fastest way to solve it? Otherwise easy

I thinks its probably fastest the way you have done

Re: easy Digits problem and Semicircle.. - fastest way to solve it? Otherwise easy

22. A and B are letters representing different digits from 1 to 9.

Given:

AB

X 7

-----

4BB

B × 7 = B

B = 0 or 5

if B = 0 then A × 7 = 40

none of value of integer value satisfy the condition

so B = 5

A 5

× 7

---------

455

calculate directly 455/7 = 65

A = 6

or A × 7 + 3 (c/f) = 45

or A × 7 = 42

A = 6

A - B = 6 – 7 = – 1

(4) -1

A certain 2 digit number is known to be 3 times as great as the sum of its digits. What is the product of its digits?

Let the digits in the number be ab

then number is 10a + b

10a + b = 3(a + b)

10a + b = 3a + 3b

7a = 2b

a = 2, b = 7

a × b = 14

2. 14

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