Question

Answer the questions in attachment​

Answer 1

Answer:

the focal length of concave lens=-f2

the focal length of convex lens=F1

here power of both=-1/F1, 1/f2

then in contact=-1/F1+1/f2

=-f2+f1/f1f2=. f1-f2/f1f2

here the power of convex lens is greater

Answer 2

Answer:

In such puzzles, first we have to find out the logic behind the sequence, so that the value mentioned can be derived mathematically.

Let us see the logic behind this puzzle. The puzzle is following a strange sequence. First the difference of middle number and first number is subtracted. Then multiplication by 10 in last number of the set to be done, then from the product, the difference of middle number and first number to be substracted to derive the final value of the set.

For illustration

Let m, n, o = p. Then first subtract m from n = (n - m) then o × 10 - value from n - m to get p

Accordingly, we have to proceed by this logic starting with first set.

1, 5, 8=76

5 – 1 = 4

8 × 10 - 4 = 76

–—

2, 7, 3 = 25

7 - 2 = 5

3 × 10 - 5 = 25

—-

3, 4, 9 = 89

4 - 3 = 1

9 × 10- 1 = 89

——

4, 5, 7 = 69

5 - 4 = 1

7 × 10 - 1 = 69

——

5, 3, 8 = ??

3 - 5 = - 2

8 × 10-(-2)= 82

Thus the numbet 82 to come in place of question mark

Answer number 82 to come in place of question mark